DbSet.Cast() Error: Cannot create a DbSet from a non-generic DbSet for objects of type 'Entity'

Question

Version Info:

I am using C# 4.5, Entity Framework 6.0, and MEF.

Code and Unit Test

I created a Test Project to expl

Answer 1

As I wasn't able to cast a generic DbSet to a typed DbSet I used instead a typed IQueryable which can do the same things I needed from the DbSet.

Here is a extension that can get you that:

    public static IQueryable<T> GetIQueryableByTableName<T>(this DbContext context, string tableName)
    {
        var type = Assembly.GetExecutingAssembly().GetTypes().FirstOrDefault(t => t.Name == tableName);
        if (type == null)
        {
            throw new Exception("GetIQueryableByTableName received an invalid table name.");
        }
        return context.GetType().GetMethod("Set", new Type[0]).MakeGenericMethod(type).Invoke(context, new object[0]) as IQueryable<T>;
    }

Answer 2

Ok i know nothing about Entity framework but from looking at the docs

http://msdn.microsoft.com/en-us/library/gg696521%28v=vs.103%29.aspx

DbSet<TEntity> item = DbContext.Set<TEntity>;

so actually your code would be the same as this:

DbSet<User> nonGeneric = context.Set<User>();

and to get a IUser

DbSet<IUser> nonGeneric = context.Set<User>();

or maybe

var generic = nonGeneric.Cast<DbSet<IUser>>();

Answer 3

For this, I would actually suggest using reflection. In the constructor of your DbContext, you can set a property to the function pointer:

method = this.GetType().GetMethod("Set", new Type[0]).MakeGenericMethod(typeof(UserImplementation));

You can then invoke this using:

method.Invoke(this, new object[0]);

And this should return an object of type DbSet<UserImplementation> which the .Cast<>() method can then be invoked on.

Answer 4

replace

nonGeneric.Cast<IUser>();

by

Enumerable.Cast<IUser>(nonGeneric);