Collection.ToList<TResult>() extension method raises compile time error

Question

I cannot use ToList<Tresult>() extension method. The code I use is,

 return this.Semesters.ToList<ISemester>()

'Semesters' in above code is an EntityCollection. These using directives are already present,

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

Still I cannot Compile as it keeps on complainting that System.Data.Objects.DataClasses.EntityCollection<Semester> does not contain a definition for 'ToList' and the best extension method overload System.Linq.ParallelEnumerable.ToList<TSource>(System.Linq.ParallelQuery<TSource>) has some invalid arguments

Answer 1

Lack of a reference to the System.Core assembly? That would probably do it...

EDIT: There has to be something in the System.Linq namespace, or that would have failed to compile. I thought that maybe PFX was making that bit work... but assuming you're using .NET 4, the ParallelEnumerable class is also in System.Core.

What happens if you type Enumerable. - does that show anything?

Answer 2

are you missing

System.Data
System.Data.DataSetExtensions
System.Data.Entity

in your references?

Answer 3

Are you sure Semester implements ISemester? As a test, I did this

interface ISemester { }
class Semester : ISemester { }

// ...

List<Semester> Semesters = new List<Semester>();
var query = Semesters.ToList<ISemester>();

Which is fine. However, change the class to simply be class Semester { }, and a syntactically-similar error to the one you reported surfaces.