Entity Framework ObjectContext with Dependency Injection

Question

Well, it seems like I'm stuck in my application structure. Here's what I want to do:

UI layer: An ASP.NET webforms website.
BLL: Business logic layer which calls the repositories on DAL.
DAL: .EDMX file (Entity Model) and ObjectContext with Repository classes which abstract the CRUD operations for each entity.
Entities: The POCO Entities. Persistence Ignorant. Generated by Microsoft's ADO.Net POCO Entity Generator.

I'd like to create an obejctcontext per HttpContext in my repositories to prevent performance/thread [un]safety issues. Ideally it would be something like:

public MyDBEntities ctx
{
    get
    {
        string ocKey = "ctx_" + HttpContext.Current.GetHashCode().ToString("x");
        if (!HttpContext.Current.Items.Contains(ocKey))
            HttpContext.Current.Items.Add(ocKey, new MyDBEntities ());
        return HttpContext.Current.Items[ocKey] as MyDBEntities ;
    }
}

The problem is the I don't want to access HttpContext in my DAL (Where the repositories are located). But I have to somehow pass HttpContext to DAL. based on the answer to my question here, I have to use IoC pattern. Ideally I'd like to achieve something like this in amulti-layered architecture.

I've checked out Autofac and it seems very promising. But I'm not sure how could I achieve this (Passing Httpcontext to make sure one ObjectContext is instantiated per HttpContext) in a multi-layered architecture. Could anyone give me some working example on how to achieve this? How can I be aware of HttpContext in DAL without directly accessing the HttpContext in DAL? I feel like I'm a bit lost in designing a multi-layered solution.

Ladislav Mrnka Ladislav Mrnka · Accepted Answer · 2011-01-06T22:22:38

I have never used IoC container with WebForms so get this as some high level solution which should probably be futher improved.

You can try creating some IoC provider as singleton:

public class IoCProvider
{
  private static IoCProvider _instance = new IoCProvider();

  private IWindsorContainer _container;

  public IWindsorContainer
  {
    get
    {
      return _container;
    }
  }

  public static IoCProvider GetInstance()
  {
    return _instance;
  }

  private IoCProvider()
  {
    _container = new WindsorContainer(new XmlInterpreter(new ConfigResource("castle")));
  }
}

Your web.config will have to contain sections like (the configuration is based on your previous post):

<configuration>
  <configSections>    
    <section name="castle" type="Castle.Windsor.Configuration.AppDomain.CastleSectionHandler, Castle.Windsor" />
  </configSections>

  <castle>
    <components>
      <component id="DalLayer"
                 service="MyDal.IDalLayer, MyDal"
                 type="MyDal.MyDalLayer, MyDal"
                 lifestyle="PerWebRequest">
        <!-- 
             Here we define that lifestyle of DalLayer is PerWebRequest so each
             time the container resolves IDalLayer interface in the same Web request
             processing, it returns same instance of DalLayer class
          -->
        <parameters>
          <connectionString>...</connectionString>
        </parameters>
      </component>
      <component id="BusinessLayer"
                 service="MyBll.IBusinessLayer, MyBll"
                 type="MyBll.BusinessLayer, MyBll" />
      <!-- 
           Just example where BusinessLayer receives IDalLayer as
           constructor's parameter.
        -->
    </components>
  </castle>  

  <system.Web>
    ...
  </system.Web>
</configuration>

Implementation of these interfaces and classes can look like:

public IDalLayer
{
  IRepository<T> GetRepository<T>();  // Simplified solution with generic repository
  Commint(); // Unit of work
}

// DalLayer holds Object context. Bacause of PerWebRequest lifestyle you can 
// resolve this class several time during request processing and you will still
// get same instance = single ObjectContext.
public class DalLayer : IDalLayer, IDisposable
{
  private ObjectContext _context; // use context when creating repositories

  public DalLayer(string connectionString) { ... }

  ...
}

public interface IBusinessLayer
{
  // Each service implementation will receive necessary 
  // repositories from constructor. 
  // BusinessLayer will pass them when creating service
  // instance

  // Some business service exposing methods for UI layer
  ISomeService SomeService { get; } 
}

public class BusinessLayer : IBusinessLayer
{
  private IDalLayer _dalLayer;

  public BusinessLayer(IDalLayer dalLayer) { ... }

  ...
}

Than you can define base class for your pages and expose the business layer (you can do the same with any other class which can be resolved):

public abstract class MyBaseForm : Page
{
  private IBusinessLayer _businessLayer = null;
  protected IBusinessLayer BusinessLayer
  {
    get 
    { 
      if (_businessLayer == null)
      {
        _businessLayer = IoCProvider.GetInstance().Container.Resolve<IBusinessLayer>(); 
      }

      return _businessLayer;         
  }

  ...
}

Complex solution whould involve using custom PageHandlerFactory to resolve pages directly and inject dependencies. If you want to use such solution check Spring.NET framework (another API with IoC container).

Entity Framework ObjectContext with Dependency Injection

1 Answers