IEnumerable的 <T> 以某种方式转换为EntitySet <T>

Question

I have an hierarchy of classes that I fetch from database by LINQ to SQL controller and the display that big class as needed.Let me explain:

BigProduct
IEnumerable<Review>
//...some generic types


Review
IEnumerable<Comment>
//...some generic types


Comment
//...some generic types

So in my controller I fetch big product and pass it to main view, then pass reviews in foreach to partial views and in each of these partial views I have another foreach that should list all comments as partial view.

The types are defined clear as Ienumerable in classes and this dll worked fine with web forms,now when I hover my mouse over Comment in foreach loop in razor it says it's EntitySet instead of IEnumerable and I get "null exception: acessed context after disposed", that was the reason I am passing it as IEnumerable in first place as I fetch everything in one place. What could be the reason for such behaviour? I didn't change anything in this dll that used to work fine with webforms.

UPDATE: As I mentioned it worked fine with WebForms, I am calling .ToList() to get IEnumerable from IQueryable in when selecting data!

Answer 1

Just because you declare it as IEnumerable<T> , that doesn't change the execution-time type. So when you pass it over to your view, the view would know at compile-time that it's IEnumerable<T> but when you hover over it when debugging, you'll see the actual type. (It's not clear at what point you were hovering over Comment in the razor view, but I strongly suspect it's in the middle of a debugging session.)

If you want to take a copy of the data so that you can dispose the context, just call ToList() and return the result - that will be a List<T> instead.

Note that this compile-time/execution-time difference has nothing to do with LINQ or MVC really. You can see the same thing extremely easily without anything complicated:

object value = "hello";

The compile-time type of value is object , which will stop you calling Substring etc on it. But if you hover over value in a debugging session (or look at it in the Watch or Local window) you'll see that the execution-time type is still string .

EDIT: From your edit:

I am calling .ToList() to get IEnumerable from IQueryable in when selecting data!

I'd really like to see that code, because I don't believe you're simply using something like:

return query.ToList();

If you're returning the result of calling ToList() , that won't be an EntitySet .

Answer 2

When you return a reference to an interface type, like IEnumerable<T> , the reference still points to the object whose run-time type implements the interface. More generally, whenever you refer to an object through an interface that it implements, or through a base class in its inheritance chain, you're still referring to an instance of the object's most-derived type.

For example:

object o1 = new object();
object o2 = "I am a string.";
object o3 = 42;

Console.WriteLine(o1.GetType());
Console.WriteLine(o2.GetType());
Console.WriteLine(o3.GetType());

IComparable ic1 = "I am a string.";
IComparable ic2 = 42;

Console.WriteLine(ic1.GetType());
Console.WriteLine(ic2.GetType());

Output:

System.Object
System.String
System.Int32
System.String
System.Int32

If you want to copy the data to another object that also implements IEnumerable<T> , you need to write some code to do that. As others have suggested, calling ToList() is an easy way to achieve this.