How do I define Foreign Key Optional Relationships in FluentAPI/Data Annotations with the Entity Framework?

Question

I have a (sample) application with the following code:

public class Posts
{

    [Key]
    [Required]
    public int ID { get; set; }

    [Required]
    pub         


        

Answer 1

The ForeignKey just has to be Nullable to make it optional - virtual is separate, and only required for Lazy Loading.

A required relationship in declarative EF Code First:

public User User { get; set; }
[ForeignKey("User")]
public int UserId { get; set; }

An optional relationship in declarative EF Code First:

public User User { get; set; }
[ForeignKey("User")]
public int? UserId { get; set; }

You'll see it when you run update-database -verbose -f:

ALTER TABLE [dbo].[MyTable] ALTER COLUMN [UserId] [int] NULL