MVC 3 and Entity Framework 4.1 data loading issue - asp.net-mvc-3

Question

Ok!
I have to say both technology are great. Although there seems that something I do not get it.
You have a data in you database (and let say you want to show data from a table that has references to other tables).
I have a model with List or IEnumerable or IQueryable or whatever...
So in my view I want do foreach through the list of object and take advantage of cool feature of references to other tables. No problem in controller while you are in
using (var datatabse = new MyEntity)
{
}
But when you get out of using db has disposed and you get common error The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
So i do not see other options as creating in memory copies of entity objects...but you loose all cool EF4 references and you have to manually load data first in your model and then with foreach show it on the view.
So instead of List<(EF4Type)> or IEnumerable<(EF4Type)> or IQueryable<(EF4Type)>
you have to do List<(MyCustomHelperClass)> where MyCustomHelperClass represents a class with properties similiar to entity objects and probably some additional beacuse you do not have access to properties of referenced tables Then you have to do foreach and Load data into this List and the another #foreach on the view with Razor to show all.
Twice as much work and if project is big...you can see a bigger picture of how manny those helperClasses you need. Was all this cool new technology really meant to be used in that way?....or am I missing something.

Answer 1

You are probably getting that error when you reference a lazy loaded property in your view. You should eager load everything you need in the Controller before passing it to the View.
See Loading Related Objects (Entity Framework).
The following example will cause all courses to be retrieved with the departments in the same query. This is eager loading.
// Load all departments and related courses
var departments1 = context.Departments
.Include(d => d.Courses)
.ToList();
Without the Include() part, courses could be retrieved later (possibly after your context has been disposed in the view). This is called lazy loading.

Answer 2

Along with eager loading as remembered by jrummell, there's also another way of loading related entries, it's explicit loading. Let's suppose you have a User entity, with many Groups entities related to it. You can explicitly load them:
var user = context.Users.Find(id); // Load the user.
context.Entry(user)
.Collection(u => u.Groups)
.Load();
This way you don't have to use the .Include(), and you can even filter the Groups:
context.Entry(user)
.Collection(u => u.Groups)
.Query()
.Where(g => g.SomeProperty.Contains("something"))
.Load();

Answer 3

TheMentor,
Depending on whether you have a repository or a db context, this object should only live for the duration of the controller action (Request), so you should be able to do everything required within the confines of the action.
Maybe i've misunderstood, but based on your question, this is what your issue appears to be. If I have misunderstood, then I'd still suggest that the db repository or db context should be referenced across the controller, rather then invoking it inside the action each time.
so you should see something like this in your controller:
public class TasksController : BaseController
{
private readonly TaskService _serviceTasks;
public TasksController(IRepository repository)
{
_serviceTasks = new TaskService(repository);
}
//
// GET: /Tasks/
public ActionResult Index()
{
var viewModel = _serviceTasks.All<Task>();
return View(viewModel);
}
public ActionResult Details(int id)
{
var domainModel = _serviceTasks.GetById<Task>(id);
var viewModel = PopulateDetailsViewModel(domainModel);
return View(viewModel);
}
//.. rest of actions cut
}