In ASP.NET MVC3 controllers, where do you instantiate your DataContext?

Question

In your ASP.NET MVC 3 applications that use a DataContext or DbContext, where do you instantiate your data access object?

Here is a non-exhaustive list of where I've seen it done:

• Individually within each method of the controller
• In the controller's constructor
• As a property (lazy-initialized) of the controller
• In an ActionFilter, shoved into ViewBag
• In Global.asax Application_BeginRequest
• In an HttpModule

I can't identify a clear front-runner amongst all of those. What's worse, whenever I start a brand-new project, I tend to change it up, just because.

Does anyone have any battle-tested advice?

Answer 1

My dependency injection framework controls the creation and lifetime of the DbContext. The instantiation usually happens when the controller (or one of its dependencies) is instantiated.

Answer 2

Basically, I store it in HttpContext.Items, instantiating it the first time it is required, and re-using it if it is needed again. The lifespan of HttpContext.Items is the lifetime of the web request, so when all work for the request is complete, the data context is finished with.

I got the idea from story three in this blog post by Steven Sanderson, which also has some neat advice for extending that idea with inversion of control so there is no hard dependency between your data layer and HttpContext.

Answer 3

For smaller projects I Basically, store it in HttpContext.Items. However, I love lazying loading, so I'm not a fan of spinning up a DBContext on literally every HttpApplication Request. So instead I wrote the following:

public static class ControllerExtensions
{
    public static MyDBContext MyDBContext(this Controller instance)
    {
        MyDBContext result = 
          instance.HttpContext.Items[typeof(MyDBContext).Name] as MyDBContext ;

        if (result == null)
        {
            result = new MyDBContext ();
            instance.HttpContext.Items[typeof(MyDBContext).Name] = result;
        }

        if (result == null)
        {
            throw new InvalidOperationException("No DBContext in HttpContext.");
        }

        return result;
    }

This means I have a Strongly-Typed, Lazy loaded, Single DBContext per Request, MyDBContext available for any controller to use.

public HomeController
{
  public ActionResult Index()
  {
    List<string> model = this.MyDBContext().Cars
                                           .Select(x => x.Name)
                                           .ToList();

    this.View(model);
  }
}