Entity Framework: field of composite key cannot be nullable?

Question

I have a model with composite key - the row is the key:

public class Item
{
    [Key, Column(Order = 0)]
    public int UserId { get; set; }
    [Key, Column         


        

Answer 1

It's not possible with Sql Server, or Oracle for any part of a primary key.

But you can have a unique constraint on these datas.

Which means you can have one time

UserId = 2, Date = null

Then

UserId = 2, Date = <NOT NULL>

You can't create directly unique constraints with Code First, but look at SMO.

Answer 2

Answer from Raphael lead me to another search. Here is the why it is not possible (answer from Cobsy):

What's wrong with nullable columns in composite primary keys?

In short: NULL == NULL -> false

Wierd. The solution for me is to add Id column into Model.

BTW: MySQL allow me not to define Primary Key, then I'm allowed to have such schema - EF complains about not defining the key :-(.

Answer 3

It is not possible. Every RDBMS requirement is, that primary key must be not nullable.