Dependency Injection & Model Binding (ASP MVC, Autofac), When to use what?

Question

This is more like a conceptual question. When to use Model Binding (in ASP.NET MVC Framework) and when to inject objects using IoC (lets say Autofac here) ?

One specific scenario is like lets say, I have the following action method

public ActionResult EditProfile(string UserId)
{
    // get user object from repository using the the UserId
    // edit profile
    // save changes
    // return feedback
}

In the above scenario, is it possible to inject a user object to action method such that it automatically gets the user object using the UserId ? The resulting signature being:

public ActionResult EditProfile(UserProfile userObj) //userObj injected *somehow* to automatically retreive the object from repo using UserId ? 

Sorry if it all doesn't makes sense. It`s my first time using IoC.

EDIT:

This is the way to do it > http://buildstarted.com/2010/09/12/custom-model-binders-in-mvc-3-with-imodelbinder/

Answer 1

You can do what you need using a custom action filter. By overriding OnActionExecuting, we have access to the route data, and the action parameters of the action that will be executed. Given:

public class BindUserProfileAttribute : ActionFilterAttribute
{
  public override OnActionExecuting(FilterContext filterContext)
  {
    string id = (string)filterContext.RouteData.Values["UserId"];
    var model = new UserProfile { Id = id };

    filtextContext.ActionParameters["userObj"] = model;
  }
}

This attribute allows us to create the parameters that will be passed into the action, so we can load the user object at this point.

[BindUserProfile]
public ActionResult EditProfile(UserProfile userObj)
{

}

You'll probably need to get specific with your routes:

routes.MapRoute(
  "EditProfile",
  "Account/EditProfile/{UserId}",
  new { controller = "Account", action = "EditProfile" });

In MVC3 we get access to the new IDepedencyResolver interface, which allows us to perform IoC/SL using whatever IoC container or service locator we want, so we can push a service like a IUserProfileFactory into your filter, to then be able to create your UserProfile instance.

Hope that helps?

Answer 2

Model binding is used for your data. Dependency injection is used for your business logic.