How to add a partial class to a edmx and use it as a navigation property to a existing entity?

I am going to create a model class of my own as a partial class. How to add this partial 开发者_如何学Cclass as a navigation property to a existing entity. Help me on this...

It doesn't matter if you created class yourselves or let some code generator to create it from EDMX file. Your hand made class still must have counter part in EDMX (the entity). Navigation properties are defined among entities in EDMX.