Why is this column getting generated in EF Code-First migrations?

问题

I have a Mentorship entity, which has Student and Mentor as FKs:

    [Required]
    public int MentorId { get; set; }
    public virtual User Mentor { get; set; }

    [Required]
    public int StudentId { get; set; }
    public virtual User Student { get; set; }

User model:

    public virtual ICollection<Mentorship> Mentorships { get; set; }

Fluent API:

    modelBuilder.Entity<Mentorship>()
        .HasRequired(c => c.Mentor)
        .WithMany()
        .HasForeignKey(u => u.MentorId);

    modelBuilder.Entity<Mentorship>()
        .HasRequired(c => c.Student)
        .WithMany()
        .HasForeignKey(u => u.StudentId);

In my database, I see StudentId and MentorId columns which have been populated correctly, but I also see a User_UserId column that is not being used by anything. What have I done wrong?

回答1:

You have used the WithMany() overload that configures the relationship to be required:many without a navigation property on the other side of the relationship - but you do have a navigation property on the other side of the relationship.

Try this:

modelBuilder.Entity<Mentorship>()
    .HasRequired(c => c.Mentor)
    .WithMany(d => d.Mentorships)
    .HasForeignKey(u => u.MentorId);

modelBuilder.Entity<Mentorship>()
    .HasRequired(c => c.Student)
    .WithMany(d => d.Mentorships)
    .HasForeignKey(u => u.StudentId);//oops! just realised that we just 
                                     //specified that Mentorships is using MentorId 
                                     //as the FK

References:

Required WithMany Method

Why do I get an extra foreign key?

Edit Scratch that. Just realised you are trying to create two relationships with only one navigation property on the many side. You can't have a navigation property with 2 foreign keys. You need to introduce inheritance on the User side or remove the Mentorships navigation property from the User class or introduce separate StudentMentorships and MentorMentorships navigation properties

Edit 2 Finding a user once you've defined separate navigation properties

int userId = 123;//the one we want to find
var user = Users.Where(x => x.StudentMentorships.Any(s => s.StudentID == userId) 
                         || x.MentorMentorships.Any(s => s.MentorID == userId);

来源：https://stackoverflow.com/questions/19802324/why-is-this-column-getting-generated-in-ef-code-first-migrations

标签

entity-framework

ef-code-first