C#: specialized template method - Error: Type '…' already defines a member called '…' with the same parameter types

Question

I\'m quite new to C# and currently developing an application using the EntityFramework. I would like to extend the functionality of the database context class, so that I can cal

Answer 1

Unfortunately, in C#, you cannot overload a method by using a generic type constraint like this. You will have to give them different names like this

public class TestContext : DbContext
{
    public DbSet ATests { get; set; }
    public DbSet BTests { get; set; }

    public IQueryable getPoolA() where T : TestA {
       return (IQueryable)ATests;
    }
    public IQueryable getPoolB() where T : TestB {
       return (IQueryable)BTests;
    }
}

Another solution would be to do something like this:

public class TestContext : DbContext
{
    public DbSet ATests { get; set; }
    public DbSet BTests { get; set; }

    public IQueryable getPool() {
       return (typeof(T) == typeof(TestA))
                  ? (IQueryable)ATests
                  : (IQueryable)BTests;
    }
}

Now, you can make this even cleaner, since IQueryable is covariant in T, you can avoid casting:

public class TestContext : DbContext
{
    public DbSet ATests { get; set; }
    public DbSet BTests { get; set; }

    public IQueryable getPool() {
       return (typeof(T) == typeof(TestA)) ? ATests : BTests;
    }
}

---

If you want to avoid testing for types you can do something like this:

public class TestContext : DbContext
{
    readonly Dictionary _sets;

    public DbSet ATests { get; set; }
    public DbSet BTests { get; set; }

    public TestContext()
    {
        _sets = new Dictionary
        {
            { typeof(TestA), ATests },
            { typeof(TestB), BTests }
        }
    }

    public IQueryable getPool() {
       return (IQueryable)_sets[typeof(T)];
    }
}