UpdateGraph fails if PrimaryKey is nullable in Entity POCO, but not null in database

[davisnw]

If you have an entity class like so:

public class Foo { Guid? Id { get; set; } }

and your database table is

create table dbo.Foo ( Id uniqueidentifier NOT NULL )

Then UpdateGraph fails with an exception that "there is no binary == operator between Guid? and Guid".

[davisnw]

(I should perhaps mention that the above scenario is motivated by the desire to clearly know the difference between a new entity and a persisted entity within the POCO object model. With a nullable id, it will default to null when an object is "newed up" clearly communicating that this is a non-persisted entity. However, an entity retrieved from entity framework will always have a non-null id).

[refactorthis]

I had a quick look at this, the expression is created at DbContextExtensions.cs:282. The comparison is written in an Expression and I can't assume a type for the Id. So it's going to be hard to know what to convert it to to ensure equality. Perhaps I can check to see if one is a Nullable and convert the other so that they are even. I'll look into this soon.