Instanciate Entity Framework context per request via Microsoft Unity in WebApi 2.0 - entity-framework

Question

I have a N-layer solution that works correctly in my dev environment. Apparently it works also on production environment, but sometime the execution fails. I do not understand why. I just know that nothing changes on database, no usefull error is visible and no log is written.
My supposition is a concurrency problem. I think that something fails when I try to do more than one select once the entity framework context has been initialized.
Here how my solution is structured
In the facade I inject the entity framework context. Here the configuration on my web.config of the service interface:
<containers>
<container>
<types>
<register type="it.MC.IContext.IDataContext, IContext"
mapTo="it.MC.EntityFrameworkContext.PublicAreaContext, EntityFrameworkContext">
<lifetime type="singleton" />
</register>
<register type="it.MC.IFacade.IPublicAreaFacade, IFacade"
mapTo="it.MC.Facade.PublicAreaFacade, Facade">
<interceptor type="TransparentProxyInterceptor" />
<lifetime type="singleton" />
<constructor>
<param name="context" type="it.MC.IContext.IDataContext, IContext"/>
</constructor>
</register>
</types>
</container>
</containers>
As you can see, my context and the facade are singleton. I think both are really wrong. I think that both Facade that the entity Framewrk context should be instanciate per request. I think this will solve the problem of the concurrency too.
Can anyone help me to correct my code please?
Thank you

Answer 1

I know that your question is:
Can anyone help me to correct my code please?
I read it like this:
Can anyone help me change this code so that IContext and IFacade will be re-initialized per request.
With that said... Yes, I also doubt that you want to keep your IContext as a singleton.
Why you shouldn't use singleton DataContexts in Entity Framework
Here's how you can change the lifetimemanager to PerRequestLifetimeManager, if that's what you want. Note that you probably need the Unity.Mvc NuGet-package.
<containers>
<container>
<types>
<register type="it.MC.IContext.IDataContext, IContext"
mapTo="it.MC.EntityFrameworkContext.PublicAreaContext, EntityFrameworkContext">
<lifetime type="Microsoft.Practices.Unity.PerRequestLifetimeManager, Microsoft.Practices.Unity.Mvc" />
</register>
<register type="it.MC.IFacade.IPublicAreaFacade, IFacade"
mapTo="it.MC.Facade.PublicAreaFacade, Facade">
<interceptor type="TransparentProxyInterceptor" />
<lifetime type="Microsoft.Practices.Unity.PerRequestLifetimeManager, Microsoft.Practices.Unity.Mvc" />
<constructor>
<param name="context" type="it.MC.IContext.IDataContext, IContext"/>
</constructor>
</register>
</types>
</container>
</containers>
Before moving to production I suggest you read this post about the PerRequestLifetimeManager.
Its purpose would be to only instantiate one instance per request,
which could (for example) prevent redundant operations and lookups
during the course of a single request.
The danger is if someone assumes that the object created is a good
place to store state during the request. The idea of dependency
injection is that a class receives a dependency (commonly an
interface) and doesn't "know" anything about it at all except that it
implements that interface.
Also, think about the Facade you got, and how it will work if it's re-initated every request. Does it perform any heavy operations at initialization? You might want to think about the lifetimemanager for that one.
UPDATE
Since you're using WebAPI you should be able to use HierarchicalLifetimeManager instead.
http://www.asp.net/web-api/overview/advanced/dependency-injection
The dependency resolver attached to the HttpConfiguration object has
global scope. When Web API creates a controller, it calls BeginScope.
This method returns an IDependencyScope that represents a child scope.
Web API then calls GetService on the child scope to create the
controller. When request is complete, Web API calls Dispose on the
child scope. Use the Dispose method to dispose of the controller’s
dependencies.
http://www.devtrends.co.uk/blog/introducing-the-unity.webapi-nuget-package
If you are registering any components that implement IDisposable such
as Entity Framework's DbContext, you will want to make sure that these
components get disposed of at the end of the request. This is achieved
by registering these components with a HierarchicalLifetimeManager.