Self referencing / parent-child relationship in Entity Framework

Question

I read quite a number of posts of programmers that run into the Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign

Answer 1

You must define the ParentId in the category class as nullable to use it as the foreign key property for an optional relationship:

public int? ParentId { get; set; }

An int property cannot take the value null and therefore cannot represent a NULL as value in a database column.