Question

I am trying to model a “User can have 0 or 1 set of preferences” where the preferences table has a primary key of UserId which is also a foreign key to the User entity, a la this post.

I want my model something like:

  public class User
  {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }

    public virtual UserPreferences Preferences { get; set; }

  }

  public class UserPreferences
  {
    [Key]
    public User User { get; set; }

    public bool SubscribedToNewsLetter{ get; set; }
  }

with config:

HasOptional(u => u.Preferences).WithRequired(l => l.User);

yields:

SetUp : System.Data.Entity.ModelConfiguration.ModelValidationException : One or more validation errors were detected during model generation:

    System.Data.Edm.EdmEntityType: : EntityType 'UserPreferences' has no key defined. Define the key for this EntityType.
    System.Data.Edm.EdmEntitySet: EntityType: EntitySet �UserPreferences� is based on type �UserPreferences� that has no keys defined.

Answer 1

You must define a key in UserPreferences:

public class UserPreferences
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int UserId { get; set; }
    public User User { get; set; }

    public bool SubscribedToNewsLetter{ get; set; }
}