Why is EF trying to insert NULL in id-column?

Question

I am writing my project using Entity Framework 4.0 (Model first). At the beginning of the project, I faced with this problem: I am trying to insert the filled object in the

Answer 1

Try to add this into your model class .cs file:

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int CategoryId { get; set; }

Or change your column CategoryId to identity:

    CategoryId int IDENTITY(1,1)