Implementing an architecture with ASP.NET MVC (Part 4) – data access
Continuing on from part3 – the business layer. In this post the focus is on data access. In part 3, I created an interface called “ICustomerRepository” and a class “CustomerRepository” which will change to actually do something. Using the repository interface, our business code can interact with it without being coupled to the technology that is used to communicate with the data store.
This post is part of a series of posts about creating an architecture when creating a line of business application with ASP.NET MVC. The business and persistence layers have nothing to do with ASP.NET MVC or any other UI technology so this approach is relevant to any .net application. The next and last post of the series will be placing the business and persistence behind a WCF endpoint.
What technology?
We have many choices in the data access area. You could have either a ODBMS or a RDBMS. If you are using RDBMS than is a pretty good assumption to say you are using MS SQL server. So what choices do you have:
ADO.NET – Simple to understand, but as your application grows you will end up writing the same code over and over unless you create your own abstraction over the top. You have to write the SQL yourself, which means you will end up with many stored procedures (sprocs). On a positive note, you have control of the SQL and you can use sprocs as a API to your database. You can shape the result set of data in your sproc so its easier to handle in the application. This is the traditional approach, personally i had been using this approach since SQL 7.0 before .NET and also back in .NET 1.0 and 1.1. days. From experience, you do write more code mapping the results of the sproc to your classes. Other ways of using ADO.NET would be to provide the SQL inline with .NET code or use typed DataSets (poor mans attempt of ORM), but these are just wrong on many counts.
Object Relational Mappers (ORMs)
ORM’s have been around for years and have got more popular of the last 2-3 years in .net world. You have two types of ORMs, the first type are based on the Active Record pattern and the next type based on the Data Mapper pattern. The active Record pattern in short is where your database table and domain class have a 1 to 1 mapping. So your domain classes mirror the database. Works well when you have a good database schema. The Data mapper is where your domains class are different from the data tables. Their are lots of ORMs available, here is a summary I the ones I know well.
NHibernate – IMHO the most powerful ORM to date, supports the data mapping pattern, been around for a while and got a big community around it and a number of tools like NHProf and Fluent NHibernate that improve the experience. Being as powerful as it is, its a bigger learning curve. It has it own methods for querying data using HQL, detached criteria as well as Linq (not fully implemented). Also NH supports many different RDBMS’s. Negatives for me are, session management and that it requires initialising when you start your application. By default uses XML mapping files (I hate writing XML, but enjoy writing XAML. Work that one out). Need a handful of DLL’s that you need to ship with your application.
Castle ActiveRecord – Personal favourite. Built on top of NHIbernate and supports the Active Record Pattern. You add attributes to your classes and properties to set up your mapping. Its simple, but you have the power of nhibernate under the hood if you need it. The session management is simplified, still requires initialisation when your application starts. The ActiveRecordMediator is so simple to use. Negatives are that it requires shipping the same DLL’s that nhibernate needs plus the the castle ones. Borrows the querying functionality from nhibernate.
Linq for SQL (DLINQ) – Very simple to use, supports the Active Record pattern. Can you attributes or XML to define the mapping. Does come with a designer/SQL metal. Personally i hand craft my domain classes as the designer gives you a lot of boilerplate code that in more cases in not needed, plus i model the domain first and not the database. Its built into the .NET framework so no external DLL’s to manage. No session management, the data contexts only needs a connection string. The data context uses transactions by default. The only querying mechanism is Linq which is fully implemented. Negatives are: Limited to SQL server and SQL CE, have to include properties in your classes that relate to foreign keys in the db.
Linq for Entities – (ADO.NET Entity framework) – Waiting for the next version of this, as the current version is data driven instead of domain driven. So for me its not an option at the moment.
Object Database Management Systems (ODBMS)
I only have experience in using one ODBMS being db4o. Using an object database in a change in mindset and is not that common across the .NET developer community, although products like db4o does have a massive community across .net and java developers. I think the reason for slow uptake is down to the fact that RDBMS have been around for 30 odd years and they have got better and vendors have changed their products to keep supporting the current market trends like XML.
Db4o – Really easy to use, requires a tiny amount of code. Uses a file either locally or on a remote server. No mapping required, you use OO in your domain so why not store it OO in the database. Supports Linq and also has other ways to query the database. Great documentation and support. Negatives… wish it was more a mainstream so i wouldn’t have to use RDBMS’s any more.
While developing a project with Db4o, you realise that you don’t think rows in a table or association tables. And what is even better, when you already have a database in place that contains data and you make changes to your classes like adding properties, do you need a database migration script? no. Some smart stuff inside db4o knows that the type has changed an handles it. You don’t lose data, it just works. This is a big positive for me. When using a RDBMS, tracking database changes in development is a pain and you need a process in place not only for development but when you deploy to other environments. if you have a bug in script it stops you from deploying your release as you need keep your scripts in sync with your code. Needless to say, when managing SQL scripts you need to make changes within a transaction so it can rollback in the event of failure and you must also write your scripts so they can be run more than once. With Db4o its a non-issue, no scripts, no process, no problems.
So what technology?
Ok enough rumbling. With my agile head on. I will chose the simplest option, which i believe its db4o.
Implementing the Repository
At the end of part 3, I created a domain class called “Customer”, the ICustomerRepository interface and a concrete implementation called CustomerRepository.
Using db4o
- So if you haven’t got db4o you can download the msi from here. I am using version 7.4 for .net 3.5.
- In the Web.Business project, add references to:
- Db4objects.Db4o.dll
- Db4objects.Db4o.Linq.dll
- System.Configuration
- One difference between using SQL server and db4o is the connection lifetime, in SQL server connections are opened and closed as quickly as possible and the connection is returned to a pool (if configured to). In db4o, this works differently. When you start your application you open the connection and keep it open until the application ends. Their are a few ways to do this, one of the common approaches i see in web applications that require initialising a database component like nhibernate and Castle ActiveRecord is that in the Global.asax, its configured in the Application_Start() method. I think this stinks, why does UI application need to know about the persistence. My preferred way is to make it happen where its needed. Because i need to ensure the lifetime is the same as the application, I use a singleton to hold the reference. Here is that class.
using System; using System.Configuration; using Db4objects.Db4o; namespace Web.Business.Persistence.Db4o { internal class DatabaseContext : IDisposable { private static DatabaseContext context; private IObjectContainer database; static DatabaseContext() { context = new DatabaseContext(); } private DatabaseContext() { database = Db4oFactory.OpenFile(Db4oFactory.NewConfiguration(), ConfigurationManager.AppSettings["DatabaseFileName"]); } public void Dispose() { database.Close(); } public static DatabaseContext Current { get { return context; } } public IObjectContainer Client { get { return database; } } } } - I have added an application setting into the web.config called “DatabaseFileName” which as you might as guessed is the path to the db4o database file.<appSettings><add key=”DatabaseFileName” value=”C:\Web\WebDb.yap”/>
</appSettings>
- Now to make the CustomerRepository use the DatabaseContext to fetch the data. The finished code looks like this.
using System.Collections.Generic; using System.Linq; using Db4objects.Db4o.Linq; using Web.Business.Domain; namespace Web.Business.Persistence { internal class CustomerRepository : ICustomerRepository { public List<Customer> FindAll() { return (from Customer customer in DatabaseContext.Current.Client select customer).ToList(); } } } - That’s it, done. Only the database is empty. Ideally in the real world you might have screens in your application that you can use to populate the database. As we don’t, i have created a test that can be run to insert data in the database.
using NUnit.Framework; using Web.Business.Domain; using Web.Business.Persistence; namespace Web.Business.Specs { [TestFixture] [Category("Integration")] public class DataIntegrationFixture { [Test] [Explicit] public void PopulateCustomers() { Customer customer = new Customer { AccountManagerName = "Mr A Manager", AccountNumber = "ABC123", City = "Some big city", Country = "UK", Name = "Big city customer" }; DatabaseContext.Current.Client.Store(customer); } } }
If you run the application, the data will be pulled from the database and displayed in the view. If this was a real application, i would create an generic abstract EntityRepository class that took a domain class as its generic type. I would make this base class use the DatabaseContext and that way i would not be repeating code.
Implementing an architecture with ASP.NET MVC (Part 3) – The business layer
Introduction
The focus of this post it to describe how I go about developing the business layer. This post follows on from my previous post ASP.NET MVC – Creating an application with a defined architecture. In my previous post, I was fulfilling a requirement to fetch a list of customers and display them on a page with ASP.NET MVC. So I will continue on with that as an example.
The Plan
- At the end of the previous post, i had an object called “CustomerAgent” that just created two instances of the “customer” object. This is going to be replaced with a call the business layer to fetch a list of customers. The business layer will be returning the customers as a message type. The CustomerAgent will map the message type to the customer object that is already defined in the “PresentationProcesses” assembly. We will drive this out with a test.
- In the business layer, we will need to respond to the call for fetching a list of customers. Our business layer will ask a “repository” to fetch customers from a datastore. The business layer will take a list of customers and map them into a message that will be returned to the caller.
- In the next post to continue on from this one, the repository will need to get the customers from somewhere and map them into instances of objects that represent a customer in the domain model. An ORM tool will simplify this process.
While implementing this plan, we will be testing the interactions between layers. We will also be registering the more types in our IOC container.
Putting the plan into action
The CustomerAgent is not under test and currently returns fake instances, so we will create a new test assembly and place the “customer agent” under test and start driving out the interaction with the business layer.
- Create a new class library in your solution called “Web.PresentationProcesses.Specs”.
- Add a project reference to the “Web.PresentationProcesses” project.
- Add file references to “Nunit.framework”, “Rhino.Mocks” and “NSpec” (or whatever unit testing framework and mocking tool use want to use).
- Add a new class (test fixture) to this new assembly called “Fetching_a_list_of_customers” and decorate it with the “[TestFixture]” attribute.
- Add a test called “Should_fetch_and_return_customers”. This test will return a list of “customers” and assert that the result was not null. At this point the test will pass as the “customer agent” is still just returning two made up instances. Here is the test (its not the final test, its going to change)
[TestFixture] public class Fetching_a_list_of_customers { private ICustomerAgent agent; [SetUp] public void SetUp() { agent = new CustomerAgent(); } [Test] public void Should_fetch_and_return_customers() { List<Customer> customers = agent.GetCustomerList(); customers.ShouldNotBeNull(); } } - Currently the “Customer Agent” is a public class, i don’t want my implementations to be public. The interface will be only way that the above layer can communicate with this. But we will still want our tests to be able to work with the concrete implementation and also so will our mocking tool. In the “Web.PresentationProcesses” assembly, open up “AssemblyInfo.cs”. Add the following lines and save and close the file.
[assembly: InternalsVisibleTo("Web.PresentationProcesses.Specs")] [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2")] - Next step, change the “CustomerAgent” class to be “internal” instead of “public”. Run our tests to verify that it all still works.
Driving out the business layer
As mentioned earlier the service is going to return data as a message type. This is going to use a very common message pattern being “Request/Response” which is also known as the “request/reply” pattern.
The business layer is going to be in its own assembly, it will run in-process to the MVC application. We could in the future without to much effort, place the business layer behind a WCF endpoint and host the business layer in another process. I personally would not to this by default, the reasons for making the business layer remote must be because you either have more than one application that interacts with the business layer tier or because of scalability. Scalability over performance its down to your applications needs, availability and size of the user base. Moving the business layer to run out of process is another blog post that i will write as the final post of this series as optional approach. Although the its not that different.
At the moment we have no business layer, so from the test i above, we start defining the interface (contract) in the business layer.
I am a big fan of Resharper, it makes my world a better place. It saddens me to think that developers are out their coding without the fruits that resharper gives.
- Back into the unit test, cutting a not such a long story to be a shorter story. I am going to set up an expectation on an interface and return a response object. I have also driven out the properties that are in the response object. The test is also asserting that the “customer” UI object is populated with the values from the response Here is the test fixture. I have created the new types within the same code file as the fixture. I do this sometimes while i am cutting new code and creating new types, then i will (“with the help of resharper”) move the classes into there own files and move them into the correct assemblies. Which i do as the next step.
using System.Collections.Generic; using NBehave.Spec.NUnit; using NUnit.Framework; using Rhino.Mocks; using Web.PresentationProcesses.Customers; namespace Web.PresentationProcesses.Specs { [TestFixture] public class Fetching_a_list_of_customers { private ICustomerAgent agent; private ICustomerService service; [SetUp] public void SetUp() { service = MockRepository.GenerateMock<ICustomerService>(); agent = new CustomerAgent(); } [Test] public void Should_fetch_and_return_customers() { FetchCustomerResponse response = GetResponse(); service.Expect(x => x.FetchCustomers()).Return(response); List<Customer> customers = agent.GetCustomerList(); customers.ShouldNotBeNull(); customers.Count.ShouldEqual(response.Customers.Count); IsMappingCorrect(response.Customers[0], customers[0]).ShouldBeTrue(); service.AssertWasCalled(x => x.FetchCustomers()); } private FetchCustomerResponse GetResponse() { return new FetchCustomerResponse { Customers = new List<CustomerInfo> { new CustomerInfo { AccountManagerName = "Mr Account Manager", AccountNumber = "ABC 123", City = "Some Town", Country = "Some Country", Name = "Happy Customer" } } }; } private bool IsMappingCorrect(CustomerInfo customerInfo, Customer customer) { return customerInfo.AccountManagerName == customer.AccountManagerName && customerInfo.AccountNumber == customer.AccountNumber && customerInfo.City == customer.City && customerInfo.Country == customer.Country && customerInfo.Name == customer.Name; } } public class FetchCustomerResponse { public List<CustomerInfo> Customers { get; set; } } public class CustomerInfo { public string Name { get; set; } public string AccountNumber { get; set; } public string AccountManagerName { get; set; } public string City { get; set; } public string Country { get; set; } } public interface ICustomerService { FetchCustomerResponse FetchCustomers(); } } - At the moment, the code will compile, but the test will fail. As mentioned in the last step, I am going to move the “FetchCustomerResponse”, “CustomerInfo” and “ICustomerService” into another assembly.
- Add a new class library to the solution called “Web.Business”
- Create a folder called “Contracts” and move the “ICustomerService” into this folder and change the namespace to match it new location.
- In the Contracts folder, add a new folder called “Messages”. Move the CustomerInfo and FetchCustomerResponse types into this new folder and change the namespaces.
- In both the “Web.PresentationProcesses” and “Web.PresentationProcesses.Specs”, add a project reference to “Web.Business”.
- The CustomerAgent needs to be able to talk to the “ICustomerService”, change the constructor of the “CustomerAgent” to be passed a reference of “ICustomerService” and hold the reference in a variable in the “CustomerAgent”. The “SetUp” on the unit test will change to pass in the service into the constructor of the “CustomerAgent”.
- Now to make the test pass, the code in the method ”GetCustomerList” in the “CustomerAgent” has been replaced to make the test pass. Here is that code for the modified “CustomerAgent” as well as the changes to the SetUp method in the test.
// Unit test [SetUp] public void SetUp() { service = MockRepository.GenerateMock(); agent = new CustomerAgent(service); } // Customer agent using System.Collections.Generic; using System.Linq; using Web.Business.Contracts; using Web.Business.Contracts.Messages; namespace Web.PresentationProcesses.Customers { internal class CustomerAgent : ICustomerAgent { private readonly ICustomerService service; public CustomerAgent(ICustomerService service) { this.service = service; } public List<Customer> GetCustomerList() { List<Customer> result = new List<Customer>(); FetchCustomerResponse response = service.FetchCustomers(); result.AddRange((from custInfo in response.Customers select new Customer { AccountManagerName = custInfo.AccountManagerName, AccountNumber = custInfo.AccountNumber, City = custInfo.City, Country = custInfo.Country, Name = custInfo.Name }).ToList()); return result; } } } - All the tests, now pass. Now to create a concrete “CustomerService”. Create a new folder in the “Web.Business” assembly called “Customers” and add a new internal class called “CustomerService”.
- Make the “CustomerService” implement the “ICustomerService” interface. We will come back to the method “FetchCustomers” later, so just throw a NotImplemented exception for minute.
- We need to register the types in the IOC container. We need to pass the IOC container to the “Web.Business” assembly so that it can register its types.
- Add a reference to Unity or what ever IOC container that you are using.
- Create a public class called “BusinessModule” and add a public method below.
public class BusinessModule { public void Configure(IUnityContainer container) { container.RegisterType<ICustomerService, CustomerService>(); } } - In the “Web.PresentationProcesses” assembly, add a reference to the “Web.Business” assembly.
- In the “PresentationProcessesModule”, in the configure method, create a new instance of the “BusinessModule” and call the “Configure” method passing in the container.
The Customer Service
Now to implement the CustomerService. The service itself is just a facade and brings its internals together to provide a simple API. The service will delegate to objects that have the responsibility to carry out required actions. In the case of the CustomerService, it will ask a repository to return a list of customers. The customers will be instances of a domain entity called “Customer”. The service will map the domain type to the message type.
I keep the domain isolated from the outside world. The only way to interact with the domain from the outside world is through a service. The service does not contain much logic, if it did it would mean that logic is not in the domain and the domain would be not be rich. A thin domain and rich services would the “anemic domain model” anti-pattern. In this example, I am pulling data out of a repository, so their is no business logic.
- Firstly, create a new class library assembly called “Web.Business.Specs” which you may have guessed is going to hold the tests for the business assembly. Add references to NUnit and Moq/RhinoMocks or what ever is your preferred mocking tool.
- We are going to be testing internal objects within the web.business project. As described earlier on in this post. Add this two lines to the assemblyInfo.cs in the “web.business” project.
[assembly: InternalsVisibleTo("Web.Business.Specs")] [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2")] - Create a new test fixture called “Fetching_customers”. Our is going to ask the service to provide a list of customers. This information will be provided a list of “CustomerInfo” objects contained in the “FetchCustomerResponse”. Here is the test.
using System.Collections.Generic; using NBehave.Spec.NUnit; using NUnit.Framework; using Rhino.Mocks; using Web.Business.Contracts; using Web.Business.Contracts.Messages; using Web.Business.Domain; using Web.Business.Persistence; using Web.Business.Services; namespace Web.Business.Specs { [TestFixture] public class Fetching_customers { private ICustomerService customerService; private ICustomerRepository customerRepository; [SetUp] public void SetUp() { customerRepository = MockRepository.GenerateMock<ICustomerRepository>(); customerService = new CustomerService(customerRepository); } [Test] public void Should_return_a_list_containing_customer_information() { List<Customer> customers = new List<Customer> { new Customer { AccountManagerName = "Mr A Manager", AccountNumber = "ABC 123", City = "Some Place", Country = "Some Island", Name = "Some Customer" } }; customerRepository.Expect(x => x.FindAll()).Return(customers); FetchCustomerResponse response = customerService.FetchCustomers(); customerRepository.AssertWasCalled(x => x.FindAll()); response.Customers.Count.ShouldEqual(customers.Count); IsMappingCorrect(response.Customers[0], customers[0]).ShouldBeTrue(); } private bool IsMappingCorrect(CustomerInfo customerInfo, Customer customer) { return customerInfo.AccountManagerName == customer.AccountManagerName && customerInfo.AccountNumber == customer.AccountNumber && customerInfo.City == customer.City && customerInfo.Country == customer.Country && customerInfo.Name == customer.Name; } } } - The above test drove out the customer Repository interface and a domain object called customer. At the moment i have added two new folders “Persistence” and “Domain” to the “Web.Business” project and place the customer object in the domain folder and repository interface in the “Persistence” folder. Getting a step ahead, i have created a concrete implementation of CustomerRepository. Here is the code for the new types:
namespace Web.Business.Domain { internal class Customer { public string Name { get; set; } public string AccountNumber { get; set; } public string AccountManagerName { get; set; } public string City { get; set; } public string Country { get; set; } } } // using System.Collections.Generic; using Web.Business.Domain; namespace Web.Business.Persistence { internal interface ICustomerRepository { List<Customer> FindAll(); } } // using System.Collections.Generic; using Web.Business.Domain; namespace Web.Business.Persistence { internal class CustomerRepository : ICustomerRepository { public List<Customer> FindAll() { return new List<Customer>(); } } } - Lastly, wire up the repository in IOC container, the configure method in “BusinessModule” class should look like this.
public void Configure(IUnityContainer container) { container.RegisterType<ICustomerService , CustomerService>(); container.RegisterType<ICustomerRepository , CustomerRepository>(); }
That’s it for this post. the next step is to use an ORM to fetch the data from the database, which will be the responsibility of the repository.
Simplicity equals elegance
Introduction
I have recently had to solve a massive problem do with architecting a next generation platform for a commercial product that will steer the development team now and into the future. This task has a history of failure and now I have stepped up to try a make things right. Some of the problems I needed to address was:
- Architecture (to SOA or not to SOA)
- Technology
- Migration plan
- Deployment
Retrospective
While brainstorming ideas about how to solve my particular problems, I went through a period of reflection. I questioned my self on all the practices that I would promote and the ones I would discard. I found this to be very healthy. Any good developer/architecture should regularly question their motives and approaches.
A lot of what we do its based on opinions, and sometimes based on other peoples opinions. I went about eliminating the opinions that were not by own. For example “Persistent arrogance”:
- Is this just an idealism?
- What benefit does it give me?
- What do I lose if I don’t have it?
- Is this something at sounds great in theory but in practice it not achievable?
- Is this something that someone has promoted to make them sound clever?
I did this over and over till I was happy that I had opinions that were my own. I reviewed programming and the industry in general and reflected on my own previous experience. One of the lessons I learnt was, it does not matter how clever someone is, what technologies you know or what pretty pieces of paper you have. Simple is best.
Just because its a dirty job doesn’t mean you need to get dirty!
I also find that top class developers generally make things complex and perceive that it is simple. Its worth having less junior developers around and present your code to them and get their feedback. Another trait that senior developers do it try to design and develop an elegance system, this leads to complexity, complexity leads to confusion, confusion leads to failure. The right thing to do it design and develop a system to be simply, then you get elegance.
What is Simple
Simple is relative, how do you measure simple? This is measured at many levels. The common place would be at code level.
Source code
Many books have been written about writing “Good” (again relative) code and writing Quality (relative again) code. Their are many things that make code “better” which makes it “simple” to understand and maintain: For example: (I have thought of many more points but a couple will do to illustrate the point)
- Name classes, methods and variables correctly and meaningful.
- Write methods that are small and concise.
- Follow the OO principles (SOLID).
- Use TDD with Test first design.
The next view would be how your code is structured and layered. If you have complex system that is all tackled up and depends on things that it shouldn’t, may be a few god objects and is a big sticky ball of mud. Then stretch it like a rubber band, pull the code about and separator it by the context that its used in. Of course, if you have a big ball of mud then I am pretty certain that you won’t have any unit tests that give you the feedback needed while you refactor. If you, like me have been unlucky and come to work on a code base that is a ball of sh** mess, then master refactorings and design patterns.
Technology
- Is the technology the right tool for the job?
- Are you using this tool, cos its someone above you tells you to?
- Do you have alternatives?
- How easy is it to recruit people with this skill?
- Its the technology you are using, just geeky and looks got on your CV?
Technology has a big part to play in simple/complex contest. Its worth reviewing what you are are using.
Architecture
Does the architecture guide you or does it constrain you. Do you have read a book to understand the architecture that you are using? if an architecture is not flexible and you need to read a book about it then is not simple and not right.
Trends and fashion
This is linked to technology and my retrospective stated above. Developers my nature enjoy learning new technologies. Developers also try to find new smarts for the way they work. This is all great, but does need to be managed, otherwise your code base will be littered with spikes and random technologies. Before long your developers will not know what the standard tools or right the processes are. Technology and processes are in and out of fashion very quickly. A big dollop of common sense is required, review technologies and process in isolation and actually use the technology and try out a process rather than reading some blog and believing it.
Its easier to understand what is not simple.
Make it simple
“Simple” does have some concrete measures but their are other measures that are unique to you and your team. You need to identify what is important to you and analyse your code to see how it scores. Making things simple it in my opinion, the most important design goal.
A point about Design patterns
I have heard people slate design patterns, i personally i love them, but some/alot of people misuse them and thats whats has started the negative press. The rule with design patterns to identify a pattern in the code not to put a patterns in the code that don’t fit. I find the power of patterns is the vocabulary. Its great describe a class’s purpose in life when stating its responsibility, for example “its an adapter” or “its a factory”. All things in moderation.
Conclusion
Keep it Simple. A easy principle to understand, but often the hardest to implement because out actions are to learn bigger more complex technologies and processes that keep pushing our careers to supposed new heights. It doesn’t matter how big someone’s brain is, can you develop code that is simple?
ASP.NET MVC – Creating an application with a defined architecture
Introduction
This post continues from this previous post. In this post I will be creating a ASP.NET MVC application using the architecture described in the previous post. I will start by laying out the requirements, driving out the behaviour through tests, implement Unity and create the layers for the UI, controller and Presentation Processes.
Since writing my previous post, I have came across a blog which contains some really good tips / best practices for ASP.NET MVC, which I recommend you read.
http://weblogs.asp.net/rashid/archive/2009/04/01/asp-net-mvc-best-practices-part-1.aspx
http://weblogs.asp.net/rashid/archive/2009/04/03/asp-net-mvc-best-practices-part-2.aspx
Requirements
So to start, we need requirements as development should be driven by requirements. In business analyst language, this is the requirement that i will be working against.
- As a user when browsing the customer feature within the application I expect to see a list of customers, each customer will contain the following information:
- Customer name
- Account number
- Account Manager
- City
- Country
Where to start
ASP.NET MVC is focused around controllers and actions. So its a natural place to start describing how you implement this architecture. On a day to day basic, I write tests first that drive out the behaviour. As my application grows, my layers become cemented. The name of classes denote the responsibility and context.
Creating the Project
I am starting with a new “Asp.Net MVC web application” project called “Web” and a test project called “Web.Specs”. My references are:
Web application
- MVCContrib – “MvcContrib.dll”.
Test Project
- NUnit – “nunit.framework.dll”.
- NBehave (using NSpec only) – “NBehave.Spec.NUnit.dll”.
- Rhino Mocks – “Rhino.Mock.dll”.
- MVCContrib – “MvcContrib.TestHelper.dll” and “MvcContrib.dll”.
Test first
Here is the test for the requirement defined above, putting the controller under test.
using System.Collections.Generic;
using System.Web.Mvc;
using MvcContrib.TestHelper;
using NBehave.Spec.NUnit;
using NUnit.Framework;
using Rhino.Mocks;
using Web.Controllers;
using Web.PresentationProcesses.Customers;
namespace Web.Specs
{
[TestFixture]
public class Browsing_a_list_of_customers
{
private CustomerController controller;
private ICustomerAgent customerAgent;
[SetUp]
public void Setup()
{
customerAgent = MockRepository.GenerateStub<ICustomerAgent>();
controller = new TestControllerBuilder()
.CreateController<CustomerController>(new object[] { customerAgent });
}
[Test]
public void Should_pass_a_list_of_customers_to_the_view()
{
var customers = new List<Customer>();
customerAgent.Expect(x => x.GetCustomerList()).Return(customers);
ViewResult result = controller.List();
result.ShouldNotBeNull();
result.AssertViewRendered().ForView(CustomerController.ListViewName);
customerAgent.AssertWasCalled(x => x.GetCustomerList());
}
}
}
This test has driven out the “CustomerController”, an interface called “ICustomerAgent” and two objects called “Customer” and “CustomerListViewModel”.
I have created another class library called “Web.PresentationProcesses” which doesn’t have any additional references. I have placed the Customer, CustomerListViewModel and the ICustomerAgent interface under a new folder called “Customers” in the Web.PresentationProcesses assembly.
The code created so far is:
//Customer.cs
namespace Web.PresentationProcesses.Customers
{
public class Customer
{
public string Name { get; set; }
public string AccountNumber { get; set; }
public string AccountManagerName { get; set; }
public string City { get; set; }
public string Country { get; set;}
}
}
//CustomerListViewModel.cs
using System.Collections.Generic;
namespace Web.PresentationProcesses.Customers
{
public class CustomerListViewModel
{
public List<Customer> Customers { get; set; }
}
}
//ICustomerAgent.cs
using System.Collections.Generic;
namespace Web.PresentationProcesses.Customers
{
public interface ICustomerAgent
{
List<Customer> GetCustomerList();
}
}
//CustomerController.cs
using System.Web.Mvc;
using Web.PresentationProcesses.Customers;
namespace Web.Controllers
{
public class CustomerController : Controller
{
private readonly ICustomerAgent customerAgent;
public const string ListViewName = "List";
public CustomerController(ICustomerAgent customerAgent)
{
this.customerAgent = customerAgent;
}
public ViewResult List()
{
var viewModel = new CustomerListViewModel
{
Customers = customerAgent.GetCustomerList()
};
return View(ListViewName, viewModel);
}
}
}
At this point the solution looks like this:
At the moment, the unit test will pass but if you run the application it will be broken because we don’t have a view and the customer controller doesn’t have a default constructor.
Creating the View
- Create a new folder called “Customer” inside the “Views” folder
- In the newly created folder, create a strongly typed view called “List” using the type “CustomerListViewModel”.
- Open up the site.master view. In the “menucontainer/menu” div, add the following under the link to the “Home/About” page.
<li><%= Html.ActionLink("List", "List", "Customer")%></li> - Add the following to the List view.
<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<Web.PresentationProcesses.Customers.CustomerListViewModel>" %>
<%@ Import Namespace="MvcContrib" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
<title>Customer List</title>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<h2>Customer List</h2>
<table cellpadding="1" cellspacing="0" border="1">
<thead>
<tr>
<th>Name:</th>
<th>Account Number:</th>
<th>Account Manager:</th>
<th>City:</th>
<th>Country:</th>
</tr>
</thead>
<tbody>
<% Model.Customers.ForEach(customer => { %>
<tr>
<td><%= customer.Name %></td>
<td><%= customer.AccountNumber %></td>
<td><%= customer.AccountManagerName %></td>
<td><%= customer.City %></td>
<td><%= customer.Country%></td>
</tr>
<% }); %>
</tbody>
</table>
</asp:Content>
The next stage is to have an IOC container resolve the dependencies for as at runtime.
Implementing Inversion of Control
Inversion of control / dependency injection has become very popular over the last couple of years and is a great practice to use. Their are a quite a few containers on the market at the moment, all are very good and apart from the common functionality that they all share. Some of the containers have unique qualities. I have mainly use Castle Windsor, Unity and Ninject. My personal favourite is Ninject because it has a simple fluent interface and contextual binding. At work we are using Unity mainly because its from Microsoft, but we do have applications that use Castle Windsor and Spring.net. I find that once you know one container its really ease to use another. Some of my fellow developers and I do experiment with different containers, although it doesn’t take long to swop them, using the Common Service Locator will make thing easier.
But before i start registering types, I common anti pattern that i have seen is that the container is defined in the web application being at the top of layer stack and then references all of the layers below it so it can add the types to the container. The solution to this is to pass via interface the container reference to each layer and allow a each layer to register its types.
- Starting from the top in the web application, new up the container and register the types that are in the web application only like the controllers.
- Then from the web application, pass the container reference to the PresentationProcesses layer via an interface. The PresentationProcesses assembly will expose a module object that accepts the container reference.
- The module in the PresentationProcesses layer will register its types and then could pass the container reference to the layer below it. If you are using WCF services to expose your service layer then the chain stops here. If your application doesn’t have external services and runs in-process then this pattern continues going down the layer stack.
Some IOC containers allow you to register types in config, code or both. Although i don’t like config anyway, using config to register types can cause problems. Typically when you are refactoring code, like renaming or moving types into other namespaces, that you miss out changing the config files. This results in exceptions at runtime.
I am going to stick with using Unity here and I am going to reference the unity assemblies and use MVCContrib unity assembly:
- Microsoft.Practices.Unity.dll
- Microsoft.Practices.ObjectBuilder2.dll
- MvcContrib.Unity.dll
The best place to get the container created and configured is from within Application object in the Global.asax. If you have used MonoRail and Castle Windsor together then this has the same usage pattern.
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;
using Microsoft.Practices.Unity;
using MvcContrib.Unity;
namespace Web
{
public class MvcApplication : HttpApplication, IUnityContainerAccessor
{
private static UnityContainer container;
public static IUnityContainer Container
{
get { return container; }
}
IUnityContainer IUnityContainerAccessor.Container
{
get { return Container; }
}
protected void Application_Start()
{
RegisterRoutes(RouteTable.Routes);
ConfigureContainer();
}
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.MapRoute("Default", "{controller}/{action}/{id}", new { controller = "Home", action = "Index", id = "" });
}
private void ConfigureContainer()
{
if (container == null)
{
container = new UnityContainer();
new PresentationProcesses.PresentationProcessesModule().Configure(container);
ControllerBuilder.Current.SetControllerFactory(typeof(UnityControllerFactory));
}
}
}
}
Creating the Agent
The next step to create a concrete class that implements the ICustomerAgent interface called “CustomerAgent”. We didn’t need to make it do any at the moment as we are still trying to get the application working at runtime. Plus when we do start making the “CustomerAgent” do something we will drive it from a test first. We will create this class next to where the interface lives.
using System;
using System.Collections.Generic;
namespace Web.PresentationProcesses.Customers
{
public class CustomerAgent : ICustomerAgent
{
public List<Customer> GetCustomerList()
{
throw new NotImplementedException();
}
}
}
I have created another class assembly called “Web.Container.Interfaces” which contains just one interface called “IModule” which looks like this.
using Microsoft.Practices.Unity;
namespace Web.Container.Interfaces
{
public interface IModule
{
void Configure(IUnityContainer container);
}
}
This class assembly only references Unity and will be referenced by other assemblies like “PresentationProcesses”.
Now to create the PresentationProcessesModule.
using Microsoft.Practices.Unity;
using Web.Container.Interfaces;
using Web.PresentationProcesses.Customers;
namespace Web.PresentationProcesses
{
public class PresentationProcessesModule : IModule
{
public void Configure(IUnityContainer container)
{
container.RegisterType<ICustomerAgent, CustomerAgent>();
}
}
}
Now to run the app, and now when you click the “list” link on the home page, you should get an “The method or operation is not implemented.” exception page, which is expected at this time. What this does prove it that the IoC is working correctly.
The next stage in this process would be drive out getting some real data from somewhere and will get returned from the CustomerAgent. Which is going to be in my follow on post, but for now we can simply new up a collection with some new’d up customer objects as shown below.
using System.Collections.Generic;
namespace Web.PresentationProcesses.Customers
{
public class CustomerAgent : ICustomerAgent
{
public List<Customer> GetCustomerList()
{
return new List<Customer>
{
new Customer
{
Name = "company1",
AccountNumber = "12345",
AccountManagerName = "mr account manager1",
City = "Some Town",
Country = "England"
},
new Customer
{
Name = "company2",
AccountNumber = "54321",
AccountManagerName = "mr account manager2",
City = "Some other place",
Country = "England"
},
};
}
}
}
Run the app
Now when you run the application, click on the “list” link in the menu. You should now get this following page.
Moving on
What we have got is an ASP.NET MVC that has unity in place to resolve types at runtime. We have types (customer and customer ViewModel) defined in the presentation processes layer that the view are bound to. The customer agent returns instances of these types.
The next steps will be to change the Customer agent to get the data from somewhere. This will be driven out via tests. This is going to be the focus on my next post.
ASP.NET MVC – Defining an application architecture
Introduction
ASP.NET MVC is creating some buzz at the moment and has been long awaited. Being a Microsoft product, MVC will be launched into the mainstream development arena and like webforms, could and hopefully will be a popular web development platform that will be around for years to come . Microsoft and some of the key players in this technology and has already got a good community going. The official ASP.NET MVC site contains some very light and quick code tutorials to illustrate the features of MVC.
Although this is all good, I do have some concerns. It starts with what developers learn, the tutorials on the official asp.net mvc site are aimed at developers at different levels and are for illustration only. They are not samples of production quality code. What is missing at the moment are the better practice and guidelines for developing line of business application which I am sure 99% of applications developed with ASP.NET MVC are going to be for.
Separating concerns
On the official ASP.NET MVC site, you will find code examples that are directly fetching data using linq for entities with linq queries directly in the controllers. Its not the responsibility of the controller to fetch data in this manor, their is at least a layer or two missing between controller and data access. My concern is that we will end up with same situation that is present in webforms where applications could be developed with most of the application logic ending up in the controllers (like code behind in webforms). ASP.NET MVC already is enforcing the separation of concerns for the view but not the controller and model. This is where the design focus is needed.
Layers and tiers
Layering software is probably one of the most basic concepts in the software development that I think is under estimated. I have seen on various projects in the past that its easy to get wrong with either too few or to many layers. I find that logical layers can be defined by separating out the concerns at a high level.
A layer is a logical grouping of code that have a common concern. A tier is typically a physical boundary like a server or client PC. A tier will contain at least one or more layers. Layers that are designed to run in the same tier typically communicate in a finely grained manor (chatty interface) where commutating across tiers should be coarse grain (chunky interface).
You must either be new to software development have lived in a cave or something if you have not heard of n-tier architecture. I mention tiers here because i one of the principles that is usually forgotten about in that, when communicating across tiers, do so in a coarse grain mannor.
High above the ground
The architecture that I am defining is nothing new, its a very common scenario using some Domain Driven Design concepts. An alternative variant of this architecture is an SOA implementation. The SOA variant would be the right choice an enterprise level application. The simpler variant of this architecture can be migrated to the SOA variant.
Conceptual logical layers (simple variant)
UI tier – This is the end users computer which will access your application via an internet browser. So the user interface layer will contain (x)html and CSS. Plus this layer could contain JavaScript, silverlight, Flex etc.
Presentation tier – In this tier, you have two layers, the controller and presentation processes. The controller layer will be invoked by the ASP.NET MVC framework in response to an http request. Your controller should do nothing more than delegate any processing to logic in the Presentation Processes layer. The Presentation Processes layer will typically request information from the service layer and process the service response by mapping the information to an object that both Presentation Processes and the controller layer know about. One of the benefits that this gives, is that you could develop your application that is decoupled from the service layer.
Business tier – This tier is very flexible in its implementation. In its most simplest form, it could be run in process on web server that will actually remove the physically boundary between the business and presentation tiers. For enterprise level implementations, this tier could be made up my many separate applications that could be distributed across many application servers. Regardless of the physically boundary, the Server layer should be thin as logic goes. The service layer provides an API to consumers. Beneath the service layer you have the domain layer that contains the business logic and represents the business model. The repository layer is bridge between your application logic and data persistence.
Persistence tier – Does what it says on the tin, this would typically be your database server(s).
SOA variant
Here is the conceptual logically layers using an SOA approach.
The key difference here is that the service layer is broken up into multiple services that provide a distinct function. SOA is a massive subject that i would not do it any justice trying to sell it, but using this approach gives you many benefits that the development investment is worth it. If you are have your business tier running out of process or on different services then WCF is the right technology for the job.
Although I have used ASP.NET MVC in the title of this post, this architecture is relevant for most technology implementations. Everything below the controller layer is plain .net code that you could put any .net view technology at the top of this architecture.
Architectural Rules
Rules are needed for any architecture, these are the common rules that I like to stick to.
- A layer can only see what is beneath it, never above it.
- A layer must only see the layer directly below it and not the layers further down the layer stack.
- Use message objects to communicate between layers that are across tiers (although, using message objects between any layer is also good).
- Limit your cross cutting concerns. (logging and security are typical candidates as a cross cutting concern. Loads of utilities classes/assemblies are not).
- Strive for low coupling – By enforcing a layer policy where you can only see the direct below helps here. Using interfaces that your concrete classes implement gives you a recipe of low coupling as with so many other benefits.
- No leaky abstractions.
Next steps
At this point while writing this post, i started to create an ASP.NET MVC application using this architecture. This post was starting to get to big so i have split it up. Here is the next post to continue on this topic.
db4o Most Valued Professional
I have today been selected as a db40 Most Valued Professional (DVP) of which I am flattered. I am flattered that other people have selected me for this. db4o has a massive community and following and its great being part of it.I am amongst approximatly 150 other DVP’s around the world which at the moment makes me feel a bit special. This recognition from the industry is going to drive and motivate me more to keep learning new techniques, acquire new skills and share them with anyone who takes time to read my posts.
ASP.NET MVC: A utility for testing secured Actions
I have come across a common scenario while developing an ASP.NET MVC application. This being testing Actions that require the user to be authorised and / or requires permissions to execute methods that are locked down with principal permissions.
Here as an example of a controller with an action that is firstly decorated with the “Authorize” attribute (ASP.NET MVC filter) that requires the user to be in a specified role.
[Authorize(Roles="Client Administrators")]
public ViewResult Edit(int clientId)
{
return View("Edit");
}
While I was writing a test for an Action that needed the user to be Authorized . I created implementations of the IIdentity and IPrincipal interfaces that I could use to satisfy this requirement. Although this worked, it was not reusable. When you set principle, you should apply it to the current AppDomain instead of the current thread as the every thread created in your AppDomain will have the principal set automatically. Once you have set the principle you cannot apply my than once as it will throw an exception. It is also a problem is you try to reset the principal to null.
To add to matters, is was not long before I needed to satisfy principal permissions. My Principal and Identity implementations needed to be more flexible.
So the answer was to create a utility that firstly set the AppDomain to use my principal implementation and allow each and every test to arrange the state of the principal. For each and every test I also want to write the minimum amount of code by only writing one line of code. This line of code would be amongst NBehave and RhinoMocks code that have their own fluent interfaces so I want my line of code to fit in with the fluent style. Below are three ways I want to my utility.
//1
TheCurrentUser.Instance.IsAuthenticated().And.IsInAllRoles();
//2
TheCurrentUser.Instance.IsAuthenticated()
.And.IsInThisRole("System admins")
.And.IsInThisRole("developers")
.And.IsInThisRole("power users");
//3
TheCurrentUser.Instance.IsNotAuthenticated();
So I started to create this utility by placing its into its own assembly. The root object is the “TheCurrentUser” object. Its the only public class in the assembly and is used as a singleton. It creates and hosts three objects references and sets the IPrincipal implementation to the current AppDomain.
using System;
using System.Security.Principal;
namespace RussellEast.Principal.Utility
{
public class TheCurrentUser
{
static readonly TheCurrentUser instance = new TheCurrentUser();
private IPrincipal principal;
private IAuthenticationOptions options;
private ISecurityContext context;
private TheCurrentUser()
{
BuildObjectGraph();
SetAppDomainPrincipal();
}
static TheCurrentUser() { }
public static IAuthenticationOptions Instance
{
get { return instance.Options; }
}
public IAuthenticationOptions Options
{
get { return options; }
}
private void BuildObjectGraph()
{
context = new SecurityContext();
principal = new FakePrincipal(context);
options = AuthenticationOptions.Create(context);
}
private void SetAppDomainPrincipal()
{
AppDomain.CurrentDomain.SetThreadPrincipal(principal);
}
}
}
The fluent interface uses a context object (that holds the state as its passed around) that is injected into various objects that are explained below. The context object implements the following interface.
using System.Collections.Generic;
namespace RussellEast.Principal.Utility
{
internal interface ISecurityContext
{
bool IsAuthenticated { get; set; }
bool IsInAllRoles { get; set; }
List<string> Roles { get; set; }
void Reset();
}
}
This is the concrete implementation of the ISecurityContext interface.
using System.Collections.Generic;
namespace RussellEast.Principal.Utility
{
class SecurityContext : ISecurityContext
{
public bool IsAuthenticated { get; set; }
public bool IsInAllRoles { get; set; }
public List<string> Roles { get; set; }
public void Reset()
{
IsAuthenticated = false;
IsInAllRoles = false;
if (Roles != null)
{
Roles.Clear();
}
}
}
}
Back to the “TheCurrentUser” object, the instance property returns an object that implements the following interface below.
(Although this object is a singleton, the pattern would be to return the singular instance of the singleton, i have not done this as the singleton does nothing but host objects and be the root object for the fluent interface.)
namespace RussellEast.Principal.Utility
{
public interface IAuthenticationOptions
{
IAuthorisationRouter IsAuthenticated();
void IsNotAuthenticated();
}
}
My concrete of the above interface is as follows:
namespace RussellEast.Principal.Utility
{
class AuthenticationOptions : IAuthenticationOptions
{
private readonly IAuthorisationRouter router;
private readonly ISecurityContext context;
private AuthenticationOptions(ISecurityContext context, IAuthorisationRouter router)
{
this.context = context;
this.router = router;
}
public IAuthorisationRouter IsAuthenticated()
{
ChangeSecurityState(true);
return router;
}
public void IsNotAuthenticated()
{
ChangeSecurityState(false);
}
private void ChangeSecurityState(bool isAuthenticated)
{
context.Reset();
context.IsAuthenticated = isAuthenticated;
}
public static IAuthenticationOptions Create(ISecurityContext context)
{
var roleAuthorisation = new RoleAuthorisation(context);
var router = new AuthorisationRouter(roleAuthorisation);
return new AuthenticationOptions(context, router);
}
}
}
As you can see from the code, the AuthenticationOptions class is passed an instance of the security context and an instance of the IAuthorisationRouter.
The responsibility of this class is to reset the context and set a new authentication value. This class also contains a “Factory Method” that is used to create an instance of this object.
The “IsAuthenticated” method returns the next link in the method chain being the “IAuthorisationRouter”.
namespace RussellEast.Principal.Utility
{
public interface IAuthorisationRouter
{
IRoleAuthorisation And { get; }
}
}
The “IAuthorisationRouter” purpose in life is to provide a linkage in the method chain. Here is the concrete implementation.
namespace RussellEast.Principal.Utility
{
class AuthorisationRouter : IAuthorisationRouter
{
private IRoleAuthorisationController roleAuthorisation;
public AuthorisationRouter(IRoleAuthorisationController roleAuthorisation)
{
this.roleAuthorisation = roleAuthorisation;
this.roleAuthorisation.Router = this;
}
public IRoleAuthorisation And
{
get { return roleAuthorisation; }
}
}
}
I am using constructor injection as much as possible. It was not so clear cut with this object as the AuthorisationRouter exposes an instance of “RoleAuthorisation” which implies that it has knowledge of it. The “RoleAuthorisation” exposes an instance of the AuthorisationRouter. So both need to know about each other. I am using interfaces to define the overall fluent interface so I want to keep it clean from any implementation that is needed to wire references to together. So the solution is to create another interface that is only used by a specific consumer (Interface Segregation Principal). Because I need two instances of different objects that need to know about each other, I have to construct one object first that then inject that into the other object when its be instantiated. Then I use a setter (setter injection) to provide the reference of the second object back to the first object.
namespace RussellEast.Principal.Utility
{
internal interface IRoleAuthorisationController :
IRoleAuthorisation, ISettableRouter
{
}
}
Here is the “ISettableRouter” interface:
namespace RussellEast.Principal.Utility
{
internal interface ISettableRouter
{
IAuthorisationRouter Router { set; }
}
}
Here is the “IRoleAuthorisation” interface.
namespace RussellEast.Principal.Utility
{
public interface IRoleAuthorisation
{
void IsInAllRoles();
IAuthorisationRouter IsInThisRole(string role);
}
}
I have a concrete class “RoleAuthorisation” that implements the “IRoleAuthorisationController” interface. Its responsibility is to manage the list of roles.
using System.Collections.Generic;
namespace RussellEast.Principal.Utility
{
class RoleAuthorisation : IRoleAuthorisationController
{
private IAuthorisationRouter router;
private readonly ISecurityContext context;
public RoleAuthorisation(ISecurityContext context)
{
this.context = context;
}
public IAuthorisationRouter Router
{
set { router = value; }
}
public void IsInAllRoles()
{
context.IsInAllRoles = true;
}
public IAuthorisationRouter IsInThisRole(string role)
{
if (!string.IsNullOrEmpty(role))
{
if (context.Roles == null)
{
context.Roles = new List<string>();
}
if (!context.Roles.Contains(role))
{
context.Roles.Add(role);
}
}
return router;
}
}
}
That’s all the interfaces and classes needed to build the fluent interface. The last objects needed is the Principal and Identity objects, which reads its values from the context.
using System.Security.Principal;
namespace RussellEast.Principal.Utility
{
class FakePrincipal : GenericPrincipal
{
private readonly ISecurityContext context;
public FakePrincipal(ISecurityContext context) : base(new FakeIdentity(context), null)
{
this.context = context;
}
public override bool IsInRole(string role)
{
if (context.IsAuthenticated)
{
return context.IsInAllRoles ? true : context.Roles.Contains(role);
}
return false;
}
class FakeIdentity : GenericIdentity
{
private readonly ISecurityContext context;
public FakeIdentity(ISecurityContext context) : base("Fake user")
{
this.context = context;
}
public override bool IsAuthenticated
{
get { return context.IsAuthenticated; }
}
}
}
}
Although a lot of code is written for the fluent interface which took two hours to build from scratch, I have a very flexible utility that I know I am going to use a lot and not just with ASP.NET MVC. The only refactoring that I want to perform is to change the name of some of the interfaces as I feel that they could be better described. To finish this post, here is an example using this utility in a unit test.
[Specification]
public void Should_be_able_to_edit_a_client()
{
ViewResult result = null;
story.WithScenario("editing a client")
.Given("an instance of the controller", () => controller.ShouldNotBeNull())
.And("the current user belongs to the 'client administrators' role", () =>
{
TheCurrentUser.Instance.IsAuthenticated()
.And.IsInThisRole("Client Administrators");
//NOTE: these two lines are not needed, just validating the utility.
Thread.CurrentPrincipal.Identity.IsAuthenticated.ShouldBeTrue();
Thread.CurrentPrincipal.IsInRole("Client Administrators").ShouldBeTrue();
})
.When("the Edit action is invoked", () =>
{
result = controller.Edit(1) as ViewResult;
})
.Then("verify that the user is directed to the right view", () =>
{
result.AssertViewRendered().ForView("Edit");
});
}
For a better understanding of the unit test above, please read this post
TDD/BDD with ASP.NET MVC
I have recently been going hammer and tongs with ASP.NET MVC. One of the selling points for ASP.NET MVC is its testability, so while I have been learning this technology, I have found a couple of annoyances.
When you create a new ASP.NET MVC project, the wizard in VS2008 asks you if you want to create a test project. If you do create the test project, you get a couple of pre made tests that really don’t portray good TDD and because you only get a couple of tests, you have low code coverage and have untested code. I have had to back peddle tests for the existing code.
For doing any development with ASP.NET MVC, the MvcContrib project is an absolute must. The MvcContrib project contains general features that really improve your development, Dependency Injection, type safety, a Grid and much more. I found that the MvcContrib examples, are so straight forward that in 60 seconds of eyeballing the code I could understand it fully.
Keeping to the subject, MvcContrib provides a library that really help when it comes to testing. I have been developing with MonoRail fairly solidly for the last 6 months or so and their are similarities between the Castle test classes and the Library from MvcContrib.
To make things more real world:
- My project is using Unity for its IoC container and I am injecting dependancies into my controllers (again the MvcContrib provides libraries that make this easy to implement).
- For writing my tests/specs, I am using NBehave, NUnit and RhinoMocks 3.5.
I started rewriting the tests for the HomeController because is was the easiest. The tests check that the controller displays the right view.
using System.Web.Mvc;
using RussellEast.Mvc.Controllers;
using MvcContrib.TestHelper;
using NBehave.Narrator.Framework;
using NBehave.Spec.NUnit;
using NUnit.Framework;
using Specification = NUnit.Framework.TestAttribute;
namespace RussellEast.Mvc.Tests.Controllers.Home
{
[TestFixture]
public class When_displaying_home_pages : SpecBase
{
private HomeController controller;
private Story story;
private TestControllerBuilder builder;
[Story]
public override void MainSetup()
{
base.MainSetup();
story = new Story("Home page");
story.AsA("user")
.IWant("to go to the home page")
.SoThat("i can start using the application");
PrepareController();
}
private void PrepareController()
{
builder = new TestControllerBuilder();
controller = builder.CreateController();
}
[Specification]
public void Index()
{
ActionResult result = null;
story.WithScenario("home index page")
.Given("the controller has been prepared", () => controller.ShouldNotBeNull())
.When("the user navigates to the index view", () => result = controller.Index())
.Then("verify that the result is correct", () => result.AssertViewRendered().ForView("Index"));
}
[Specification]
public void About()
{
ActionResult result = null;
story.WithScenario("about page")
.Given("the controller has been prepared", () => controller.ShouldNotBeNull())
.When("the user navigates to the about view", () => result = controller.About())
.Then("verify that the result is correct", () => result.AssertViewRendered().ForView("About"));
}
}
}
The controller code is:
public class HomeController : Controller
{
[Authorize, DefaultAction]
public ActionResult Index()
{
ViewData["Title"] = "Home Page";
ViewData["Message"] = "Sample text being displayed";
return View("Index");
}
public ActionResult About()
{
ViewData["Title"] = "About Page";
return View("About");
}
}
Note: to order for the above tests to pass, you need to supply the name of the view to render.
The tests above cover the behaviours for the HomeController which are very basic, so to raise the bar. The ASP.NET MVC project template comes with an AccountController that works with a membership provider and Forms Authentication. The controller has a constructor that accepts two parameters. Because the “System under test” is the Account Controller i am going to stub the dependencies and write tests for the “Login” and “Logout” actions.
using System.Web.Mvc;
using System.Web.Security;
using RussellEast.Mvc.Controllers;
using MvcContrib.TestHelper;
using NBehave.Narrator.Framework;
using NBehave.Spec.NUnit;
using NUnit.Framework;
using Rhino.Mocks;
using Specification = NUnit.Framework.TestAttribute;
namespace EWS.Steeple.Tests.Controllers.Authentication
{
[TestFixture]
public class When_authenticating : SpecBase
{
private AccountController controller;
private IFormsAuthentication formsAuthentication;
private MembershipProvider membershipProvider;
private Story story;
[Story]
public override void MainSetup()
{
base.MainSetup();
story = new Story("Authenticating");
story.AsA("known user to the system")
.IWant("to be authenticated")
.SoThat("i can use the system");
PrepareController();
}
private void PrepareController()
{
TestControllerBuilder builder = new TestControllerBuilder();
formsAuthentication = MockRepository.GenerateStub();
membershipProvider = MockRepository.GenerateStub();
controller = builder.CreateController(new object[] {formsAuthentication, membershipProvider});
}
[Specification]
public void Should_log_in_with_user_name_and_password_while_not_caching_details()
{
string username = string.Empty;
string password = string.Empty;
bool rememberMe = false;
ActionResult result = null;
story.WithScenario("log in with validate details")
.Given("a controller instance", ()=> controller.ShouldNotBeNull())
.And("a user name", () => username = "Username")
.And("a password", () => password = "password")
.When("i attempt to log in", () =>
{
membershipProvider.Expect(x => x.ValidateUser(username, password)).Return(true);
formsAuthentication.Expect(x => x.SetAuthCookie(username, rememberMe));
result = controller.Login(username, password, rememberMe, string.Empty);
})
.Then("redirect user to the home page", () =>
{
result.AssertActionRedirect().ToAction(x => x.Index());
formsAuthentication.VerifyAllExpectations();
membershipProvider.VerifyAllExpectations();
});
}
[Specification]
public void Should_sign_out_and_return_to_login_when_logging_out()
{
ActionResult result = null;
story.WithScenario("log out and return to login view")
.Given("a controller instance", () => controller.ShouldNotBeNull())
.When("i log out", () =>
{
formsAuthentication.Expect(x => x.SignOut());
result = controller.Logout();
})
.Then("i expect to be sent to the login view", () =>
{
result.AssertActionRedirect().ToAction("Login");
formsAuthentication.AssertWasCalled(x => x.SignOut());
});
}
}
}
Some points to be aware of.
- I have used two different ways to test the ActionResult was a redirect. The first and my preferred way is using the generic controller type and the lambda expression. I have been forced to use the string argument approach due to the fact that the “Login” action is overloaded. It complained when trying to use a lambda approach.;-(.
- MvcContrib test library provides a “TestControllerBuilder” that not only creates that instance of the controller, but mocks out the HttpContext, Sessions and form data. The docs for MvcContrib explains all. I have used this in my “PrepareController” method.
- The default code in the AccountController has not been changed to suit these tests.
Creating Fluent finders and repositories part 1
Introduction
This is the first post of this series about implementing fluent finders and repositories, I am going to expand my current repository and finder implementation which is explained here. I recommend that you read this post (precursor) as this series continues on from this post and the code examples.
The objectives for this series are:
- Create a fluent interface on the finders
- Chain the find methods so that you can find on more than one method (method chaining).
- Create an interface for sorting.
- Create an interface for paginating the results.
- Allow a service request (coarse grain) to be mapped to a specific fluent-interface call.
- Based on information provided to a service as a request object, determine the right strategy for satisfying the request.
- Execute the relevant strategy to perform the relevant queries
- Return the query results to service method that was called.
- The service method will return results as a response object.
- Drive out these behaviours using TDD/BDD.
The outcome of this work will allow you write something like:
repository.find.ByThis(somevalue).AndFind.ByThat(someOtherValue).SortBy(aField, InAscendingOrder).Paginate.WithPageSize(10).ShowPage(1);
Before I start, one of the main benefits of a fluent interface is that you create an API that guides and limits the decisions that can be expressed in a logical order. So the interface needs to limit the options as the expression flows, which ultimately means you need to plan out the branching and the interfaces for each branch and decisions to ensure that public interface is meaningful to its context.
Table of Contents
Precursor
Part 1 (this post)
- Refactoring the existing interfaces to provide interface segregation.
- The Query Command
- Method Routing
- Method Chaining
Refactoring
Following on from the precursor, I need to stop my “IApplicationUserFinder” from implementing the “IEntityFinder” interface. The reason for this is the the “IEntityFinder” interface exposes a property called DataSource. The published Fluent interface will want to expose the Find methods but not the DataSource property. So a bit of interface segregation is needed here to expose the right interface to the relevant consumer. While doing this refactoring, I decided that the name of the “IEntityFinder” is not right so I have renamed it to “IQueryableDataStore”. Although I have changed these interfaces around my concrete class ApplicationUserFinder still need to implement both. So I have created yet another interface called “IQueryableApplicationUserFinder” which implements the “IQueryableDataStore” and “IApplicationUserFinder” interfaces. Now the ApplicationUserFinder class just implements IQueryableApplicationUserFinder. If I have scrambled your brain up, hopefully the code snipets below will make things clear.
public interface IQueryableDataStore where Entity : EntityBase // was IEntityFinder
{
IQueryable DataSource { get; set; }
}
...
public interface IQueryableApplicationUserFinder :
IApplicationUserFinder,
IQueryableDataStore
{
}
...
public class ApplicationUserFinder : IQueryableApplicationUserFinder
...
Now, how is this used. The ApplicationUserFinder is injected into the ApplicationUserRepository and then exposed via a getter (all by interfaces). With the “IQueryableApplicationUserFinder” now in play, here is the revised code snippet for the repository (remember to change your IoC container to accommodate these changes).
public class ApplicationUserRepository : EntityRepository,
IApplicationUserRepository
{
private readonly IQueryableApplicationUserFinder finder;
public ApplicationUserRepository(IPersistanceRepository repository,
IQueryableApplicationUserFinder finder) : base(repository)
{
this.finder = finder;
this.finder.DataSource = Query();
}
public IApplicationUserFinder Find
{
get { return finder; }
}
}
At this point, all my unit tests pass and application runs the same as it did before this refactoring.
The Query Command
Regardless of the expression that you can write using the fluent-interface, it needs an end at some point. The Query Command objects is responsible for executing the query and return the result. I am using “Linq for objects” to write my queries and passing an IQueryable around under the covers, the execution of the queries is deferred until a method is called on it like “ToList()”. Calling the “ToList()” method will execute the underlying query. I have created a command object (based on the command pattern) to expose an “Execute” method that is going to return an IEnumerable<Entity>. The reason for returning “IEnumerable<Entity>” is that you have a vast about of extension methods that you use to execute the query. For example “ToList()” and “FirstOrDefault”. We can create the Query Command now and integrate it into the fluent-interface later with out much effort.
public interface IQueryCommand where Entity : EntityBase
{
IEnumerable Execute();
}
public class QueryCommand : IQueryCommand
{
private readonly IQueryableDataStore queryableDataStore;
public QueryCommand(IQueryableDataStore queryableDataStore)
{
this.queryableDataStore = queryableDataStore;
}
public IEnumerable Execute()
{
return queryableDataStore.DataSource.AsEnumerable();
}
}
So how can the fluent-interface get to this endpoint? Answer: we need an object to return it, so we can call it. I have defined this as “MethodRouter”.
Method Router
The method router exposes the actions that could be performed after a find method is called. As this is based on my previous post Implementing the Repository and Finder Pattern, I am going to change the original unit tests to drive out the method router. Here is the original specification for the “ApplicationUserFinder” class.
[TestFixture]
public class When_executing_queries_against_application_users
{
private ApplicationUserFinder finder; // subject under test
[SetUp]
public void Setup()
{
finder = new ApplicationUserFinder();
finder.DataSource = GetStubbedCollection();
}
[Test]
public void Should_return_a_user_by_login_name_when_supplied_a_known_login_name()
{
ApplicationUser result = finder.ByLoginName("Test.User3");
Assert.That(result.LastName, Is.EqualTo("User3"));
}
[Test]
public void Should_return_a_user_by_token()
{
ApplicationUser result = finder.ByToken(Guid.Empty);
Assert.That(result.LastName, Is.EqualTo("User2"));
}
[Test]
[ExpectedException(typeof(ArgumentNullException))]
public void Should_fail_if_supplied_null_login_name()
{
IQueryable users = GetStubbedCollection();
ApplicationUser result = finder.ByLoginName(null);
}
private IQueryable GetStubbedCollection()
{
List users = new List
{
new ApplicationUser { FirstName = "Test", LastName = "User1", LoginName="Test.User1", Token = Guid.NewGuid() },
new ApplicationUser { FirstName = "Test", LastName = "User2", LoginName="Test.User2", Token = Guid.Empty},
new ApplicationUser { FirstName = "Test", LastName = "User3", LoginName="Test.User3", Token = Guid.NewGuid()},
new ApplicationUser { FirstName = "Test", LastName = "User4", LoginName="Test.User4", Token = Guid.NewGuid()},
new ApplicationUser { FirstName = "Test", LastName = "User5", LoginName="Test.User5", Token = Guid.NewGuid()}
};
return users.AsQueryable();
}
}
As you can see from the above tests, each find method returns the result as a single domain entity. I now want to return an interface of the Method Router instead. The Method Router at point will expose the QueryCommand so that I still execute the queries and keep the code in a “close to working” state at all times.
To start with, I defined the MethodRouter interface “IApplicationUserFinderActions”
public interface IApplicationUserFinderRouter
{
IQueryCommand Output { get; }
}
Now, I need to change the return types in the IApplicationUserFinder to now return the IApplicationUserFinderRouter instead.
public interface IApplicationUserFinder
{
IApplicationUserFinderRouter ByLoginName(string loginName);
IApplicationUserFinderRouter ByToken(Guid token);
}
At this point, things a little broken, so I need to change the concrete ApplicationUserFinder class to implement the changes made to the interface. To do this the concrete finder will need to know about the Method Router class. The method Router’s responsibility is to act as a hub to link object instances together. With this in mind, the MethodRouter class will need to know about the finder and the QueryCommand class. Still being mindful of the fluent interface and members it exposes, I need to ensure that the QueryCommand knows about the IQuerable instance held in the finder without coupling the objects together. To achieve this, I going to use the same technique I used in the Refactoring effort being the i return different interfaces to different parties. I have created another interface “IFindableApplicationUserFinderRouter” that implements IApplicationUserFinderRouter with an additional member.
Here is the new interface
public interface IFindableApplicationUserFinderRouter
: IApplicationUserFinderRouter
{
IQueryableApplicationUserFinder Finder { get; set; }
}
Here is the concrete class ApplicationUserFinderRouter at this point.
public class ApplicationUserFinderRouter : IFindableApplicationUserFinderRouter
{
private IQueryCommand queryCommand;
public IQueryableApplicationUserFinder Finder { get; set;}
public IQueryCommand Output
{
get
{
if (queryCommand == null)
{
queryCommand = new QueryCommand(Finder);
}
return queryCommand;
}
}
}
Here is the changed ApplicationUserFinder
public class ApplicationUserFinder : IQueryableApplicationUserFinder
{
private readonly IFindableApplicationUserFinderRouter router;
private IQueryable users;
public ApplicationUserFinder(IFindableApplicationUserFinderRouter router)
{
this.router = router;
this.actions.Finder = this;
}
public IQueryable DataSource
{
get { return users; }
set { users = value; }
}
public IApplicationUserFinderRouter ByLoginName(string loginName)
{
if (string.IsNullOrEmpty(loginName))
{
throw new ArgumentNullException("loginName");
}
users.Where(u => u.LoginName == loginName).FirstOrDefault();
return router;
}
public IApplicationUserFinderRouter ByToken(Guid token)
{
users.Where(u => u.Token == token).FirstOrDefault();
return router;
}
}
Here is a snippet of how one of the unit tests is looking.
[SetUp]
public void Setup()
{
router = MockRepository.GenerateStub();
finder = new ApplicationUserFinder(router);
finder.DataSource = GetStubbedCollection();
}
[Test]
public void Should_return_a_user_by_login_name_when_supplied_a_known_login_name()
{
ApplicationUser result = finder.ByLoginName("Test.User3").Output.Execute().FirstOrDefault();
Assert.That(result.LastName, Is.EqualTo("User3"));
}
At this stage is hard to see the advantage of this apart from separating out code. The next step is to allow the find methods to be chained together (method chaining).
Method Chaining
The IApplicationUserFinderRouter interface is going to allow the finder to be returned from a property. This is pretty simple stuff. Below is the interface with the new property and the concrete class implementing this addition member.
public interface IApplicationUserFinderRouter
{
IQueryCommand Output { get; }
IApplicationUserFinder AndFind { get; }
}
public class ApplicationUserFinderRouter : IFindableApplicationUserFinderRouter
{
private IQueryCommand queryCommand;
public IQueryableApplicationUserFinder Finder { get; set;}
public IQueryCommand Output
{
get
{
if (queryCommand == null)
{
queryCommand = new QueryCommand(Finder);
}
return queryCommand;
}
}
public IApplicationUserFinder AndFind
{
get { return Finder; }
}
}
This now allows the find methods to be chained so you can write the following code
[Test]
public void Should_return_a_user_when_finding_by_Login_name_and_token()
{
ApplicationUser result = repository
.Find.ByToken(Guid.Empty)
.AndFind.ByLoginName("Test.User2")
.Output.Execute().FirstOrDefault();
Assert.That(result.LastName, Is.EqualTo("User2"));
}
That concludes this post, the next part of this series will cover paginating the results returned from the underlying query.
A recap on MV? pattern
I have my ever growing pet project that I have been playing about with for the last year. Its main purpose is a learning tool where I can try a few things out etc. I have been dabbling with the following view technologies.
- WPF
- Silverlight
- Winforms
- MonoRail
- ASP.NET MVC
A common saying I here a lot is ” One Architecture can not fit them all”, this is very true. I learnt a long time ago, that development is not about technology, its about principles and practices. I follow guidance from the OO and agile worlds. In these worlds, we have design patterns. The granddaddy pattern of them all is MVC. I have used MVC for years with varying technologies but mainly with winforms.
Although MVC as pattern is not technology driven, its fare to say that you would want to get the best out of the view technology that you are using. To do this, you have to use an MVC variation/implementation that suits that technology. For example, the best technology on the list above for data binding is WPF, so if you want to lever the data binding in WPF then implement either the MVVM / Presenter Model, Supervising controller patterns.
I started using WPF at first, and I admit, I got caught up in an implementation that brought the best out of WPF. I was quite pleased with myself. I used the MVVM pattern, used XAML throughout my views had no code behind (apart from implementing an interface so I could pull it from my IoC container).
Then along come silverlight 2.0 and I thought I would have a play. In was not nice, downsizing the data-binding, lack of commands etc. Bottom line, its another technology, I had to implement another variation of MVC to get the best out of silverlight. This was of course was not desirable.
Although my project is purely for play time, I have no deadlines to meet, but I was getting frustrated with the little progress I have made over a number of weeks plus adding up the learning time I was burning up with WPF and Silverlight. So I decided to help me bash some more code out and flush out my UI requirements I started to create my views in winforms. The tactic was to build a working prototype in winforms and then revisit either silverlight or WPF at a later date and swap the views out.
Now by this time, I did not want to use the data binding in winforms (another story). So crack open another MVC implementation, this time I favoured Passive view (MVP). I wanted to keep my views as dumb as possible (which is good goal to have) and drive my views and presenter logic out using TDD. I found this to be the quickest pattern to code. In this pattern, the presenter tells the view what to do via an interface that the view implements. Although this means putting code in the code behind, I found that I was only using one line of code in each method and using simple property getters and setters.
On reflection of putting in winforms, I found that I was still getting the best from the technology and it felt cleaner. I am in good position now to plug in WPF again and keeping my presenters the same. But I have parked that idea for the time being while I build up some knowledge about ASP.NET MVC. I have been doing MonoRail development for the last 6 months so its not that strange to me.
Question: Do I want to develop new controllers and actions in ASP.NET MVC or reuse my existing presenters? Answer: its worth a go, and see if I integrated them to work with each other 
To conclude. The big thing that I have learned from this effort is to use the right patterns where needed and don’t be driven by technology, stick to patterns and concepts instead, because they last longer then any technology.
