LINQ to SQL Association - "Properties do not have matching types"

Question

Hi,

I am trying to link two fields of a given table to the same field in another table. I have done this before so I can't work out what is wrong this time.

Anyway:

Table1
- Id (Primary)
- FK-Table2a (Nullable, foreign key relationship in DB to Table2.Id)
- FK-Table2b (Nullable, foreign key relationship in DB to Table2.Id)

Table2
- Id (Primary)

The association works for FK-Table2a but not FK-Table2b. In fact, when I load into LINQ to SQL, it shows Table2.Id as associated to Table1.Id. If I try and change this, or add a new association for FK-Table2b to Table2.Id it says: "Properties do not have matching types".

This also works in other projects - maybe I should just copy over the .dbml?

Any ideas?

Answer 1

No idea on the cause, but I just reconstructed my .dbml from scratch and it fixed itself. Oh for a "refresh" feature...

Answer 2

I had the same problem. This error appeared when I tried to link different types of fields, or when I tryied to drag-and-drop table to .dbml space, but .dbml already had contained linked tables with different types of linked fields.

Answer 3

I see this problem when I try to create one-to-one relationships where one side of the relationship is nullable (so really, one-to-zero/one). LINQ-to-SQL doesn't seem to support this so it appears we are forced to a plural relationship and a collection that will contain zero or one items. Annoying.