Question

I am looking to create Extension classes that extend Entity Framework Entities in a different assembly to the EF Entities. I also want to code gen some additional/generic methods in an extension methods class (using T4), then have the ability to create a partial extension methods class with additional custom methods. Is this possible.

Answer 1

You don’t need them. Just write another extension class.

namespace Namespace1
{
    public static class MyEntityBlibblingExtensions
    {
        public void Blibble(this MyEntity self)
        {
            // ...
        }
    }
}

Then, elsewhere…

namespace Namespace2
{
    public static class MyEntityFurtlingExtensions
    {
        public void Furtle(this MyEntity self)
        {
            // ...
        }
    }
}

Anything importing Namespace1 will see the extension method Blibble() while anything importing Namespace2 will see Furtle(), and importing both will see both. They can be in different assemblies or anywhere which imports MyEntity‘s namespace. So, partial extensions aren’t really a valid concept. In fact, the very idea of putting extension methods inside classes is a bit of a hack as it is – a shame they couldn’t unbend C#’s rules enough to let extension methods live outside of classes.