Code First EF5：One-to-Zero-One关系不起作用

Question

None of the similair questions seem to be able to solve this problem. I'm using Entity Framework 5, MVC 4, .NET 4.5 for my web app, designed with VS 2012.

I have 2 classes that are supposed to be in a parent-child relationship.

[Table("UserProfile")]
public class UserProfile
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }

    // Other stuff

    public int? JoggerId { get; set; }
    public virtual Jogger Jogger{ get; set; }
}

and

 public class Jogger
{
    [Key]
    public int JoggerId { get; set; }

    [Required, ForeignKey("UserId")]
    public int UserId { get; set; }
    public virtual UserProfile UserProfile { get; set; }
}

With Fluent API:

 protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {

        modelBuilder.Entity<UserProfile>()
            .HasOptional(x => x.Jogger)
            .WithRequired(c => c.UserProfile)
            .WillCascadeOnDelete(true);

        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        base.OnModelCreating(modelBuilder);
    }

A User can be a Jogger but can also not be a Jogger ie one User to zero or one Jogger. the relationship looks fine on the EF Powertools edmx view but I cannot get the Foreign key to work with the UserProfile UserId.

Is my Fluent API wrong or is it my models? Please help - I am truly stuck!

Answer 1

Your mapping with Fluent API is OK, but remove the UserProfile.JoggerId and the Jogger.UserId properties from your model and it should work. The reason is that Entity Framework uses the primary key of Jogger as the foreign key to UserProfile , so you don't need to (and can't) have a separate foreign key property. This kind of one-to-one relationship is called " Shared Primary Key Association ".

Edit

Keep in mind that the primary key of Jogger (as the dependent of the relationship) is not autogenerated in the database, only the primary key of UserProfile is autogenerated (as the principal of the relationship).

The way how you would insert a UserProfile or a Jogger or both into the database is the following:

• If you want to insert a UserProfile without a Jogger just add it to the context:

   using (var context = new MyContext()) { var newUserProfile = new UserProfile(); // no key needs to be supplied, the DB will take care context.UserProfiles.Add(newUserProfile); context.SaveChanges(); } 

• If you want to insert a UserProfile with a Jogger in a single step:

   using (var context = new MyContext()) { var newUserProfile = new UserProfile { Jogger = new Jogger() }; // no key needs to be supplied, neither for UserProfile // nor for Jogger, the DB will take care context.UserProfiles.Add(newUserProfile); context.SaveChanges(); } 

• If you want to insert a Jogger (and it must be a Jogger for an existing UserProfile ):

   using (var context = new MyContext()) { var newJogger = new Jogger { JoggerId = someExistingUserProfileId }; // a valid key needs to be supplied, otherwise you would violate a FK // constraint in the database context.Joggers.Add(newJogger); context.SaveChanges(); } 

Edit 2

For your use case where you don't have the UserId directly available but the Name (as authenticated user) instead you must load the key or the UserProfile first from the database:

// we are in an ASP.NET MVC controller action here
using (var context = new MyContext())
{
    string userName = User.Identity.Name;
    int? userId = context.UserProfiles
        .Where(u => u.Name == userName)
        .Select(u => (int?)u.UserId)
        .SingleOrDefault();

    if (userId.HasValue)
    {
        var newJogger = new Jogger { JoggerId = userId.Value };
        context.Joggers.Add(newJogger);
        context.SaveChanges();
    }
}

Or loading the UserProfile will work as well:

using (var context = new MyContext())
{
    string userName = User.Identity.Name;
    UserProfile userProfile = context.UserProfiles
        .Where(u => u.Name == userName)
        .SingleOrDefault();

    if (userProfile != null)
    {
        userProfile.Jogger = new Jogger();
        // I believe you don't need to set the JoggerId key now,
        // I'm not sure though

        context.SaveChanges();
        // Change tracking recognizes the new Jogger
        // no context.Joggers.Add is required
    }
}