Creating new entities in a layered project without getting lost in multiple HttpContext sessions

Question

I have a pretty straightforward ASP.NET MVC project built with Entity Framework and Entities->Repositories->Services->Controllers->Views layered structure. Dependency Injection is utilized.

I need to do something like this in my controller logic (Simplified for the example sake):

           var keyWord = _keywordService.GetByName("blah"); // Service instances are registered by dependency injection
           var myFile = new MyFile()
            {
                FileName = "//FilePath/etc"
            };               
           var myContent = new MediaContent()
            {
                UploadedFile = myFile
            };
           myContent.KeyWords.Add(keyword);
           _MediaContentService.AddContent(myContent); // Service instances are registered by dependency injection

But I can't. This does not work because apparently every time a new instance of an object is created ( myFile, MyContent ) - a new session of DBContext gets created with it. So when I try to save myContent, from the example, multiple Contexts conflict and I end up getting one of the two error messages:

a) An entity object cannot be referenced by multiple instances of IEntityChangeTracker. OR b) The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects.

I understand why this happens though. Every time a new instance of an EF entity is created my DBContext initializer is called and a new Context gets created. Can this be avoided ? Here is my custom DBContext:

public class MyCustomDBContext : IdentityDbContext<ApplicationUser>
{
    public MyCustomDBContext (): base("ConnStringName", throwIfV1Schema: false){}

    public static MyCustomDBContext Create()
    {
        return new MyCustomDBContext();
    }
            public DbSet<FirstEntity> FirstEntity{ get; set; }
            //Other entities
            .
            .
            .

}

And here is how that call is initialized at Startup.Auth initially. This is how the application knows where to go to create new Contexts per request:

   public void ConfigureAuth(IAppBuilder app)
    {
        // Configure the db context to use a single instance per request
        app.CreatePerOwinContext(MyCustomDBContext.Create);
    }

It looks like that Create() method keeps initializing new Context instances... I don't understand how to solve it without breaking the separation of concerns? I don't want to have to pass around an existing instance of DBContext around all layers of the application. Like This question, for example, provided a suggestion to create an instance of DBContext in the controller and then pass it down to services, repositories, etc. This suggestion does not work with built out MVC infrastructure.

As I tried in the first example, how can I create, process and link together new objects, and then send them down to services to be saved without getting lost in multiple Contexts? After all, I should only have one context per request.

Answer 1

What you should do, is use the using keyword for your solution, which will solve your problem. I use it with multiple contexes in my project:

using (MyFile myFile = new MyFile()) 
{
   using(MediaContent myContent = new MediaContent())
   {
     myFile.FileName = "//FilePath/etc";  
     myContent.UploadedFile = myFile;   

       myContent.KeyWords.Add(keyword);
      _MediaContentService.AddContent(myContent);  
   }
}

Answer 2

The solution was to create a mapping for DBContext in the dependency injection mapping file:

kernel.Bind<MyCustomDBContext>().ToSelf().InRequestScope();