Entity Framework ObjectContext with Dependency Injection - asp.net

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.

Answer 1

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).