Differences between .CreateObjectSet<T>, .Set<T>, and .CreateQuery<T>?

Question

I am writing a generic repository for entity framework and am confused as to what the difference between these calls are:

ObjectContext.CreateObjectSet<T>
ObjectContext.CreateQuery<T>
DbContext.Set<T>

I want a generic repository that both supports context generated from .edmx files as well as code first DbContext, so I've got this:

 public abstract class EntityRepository<TClass>
   where TClass : class, new()
{
    //private readonly TContext _context;
    private readonly ObjectSet<TClass> _objectSet;

    protected EntityRepository(IObjectContextAdapter context)
    {
        _objectSet = context.ObjectContext.CreateObjectSet<TClass>();

    }

    protected EntityRepository(ObjectContext context)
    {
        _objectSet = context.CreateObjectSet<TClass>();
    }

    public ObjectSet<TClass> Query()
    {
        return _objectSet;
    }
}

In the examples I have seen online I've seen all 3 used, what is the actual differences between them? Is one better performance wise? I know you can write LINQ queries against the contexts using all 3 methods.

Answer 1

The CreateObjectSet<T> returns you ObjectSet<T> that's basically collection of T objects, with ability to add, remove, ... object from this collections resulting later to inserts, deletes, ... You can also use it for querying. It's like a top level root for given entity.

The CreateQuery<T> gives you ObjectQuery<T>, which can be viewed like IEnumerable<T> (it's also IQueryable<T>). This object is like subset of ObjectSet<T> (some conditions etc.), but you can't add items to it and so on.

And finally the Set<T> returns DbSet<T> that's simplified version of first method/object for Code First. It's easier to, for instance, to use these objects (or better to say interfaces; IDbSet<T>) for i.e. unit testing etc. Similar to what ObjectContext and DbContext is.