实体框架关系错误

Question

I get the following error when using Entity Framework:

Unable to determine the principal end of an association between the types
'xxx.Domain.Entities.UserSettings' and 'xxx.Domain.Entities.User'. The 
principal end of this association must be explicitly configured using either 
the relationship fluent API or data annotations.

Here are the two Entity classes:

public class User
{
    [Key, Column("un")]
    public string Username { get; set; }
    public int Level { get; set; }

    public virtual UserSettings UserSettings { get; set; }
}

public class UserSettings
{
    [Key]
    public string Username { get; set; }
    public int ActiveRefresh { get; set; }

    [ForeignKey("Username")]
    public virtual User User { get; set; }
}

I am not sure how to resolve this error. I am stuck with the database design so I can't update that to fix the issue. Is there a way using Fluent Api to get these associations working?

A User can have a UserSettings object. This is the relationship that is desired.

Answer 1

It looks like you need a one to zero-or-one relationship

// Configure the primary key for the User
modelBuilder.Entity<User>() 
    .HasKey(t => t.Username); 

// Map one-to-zero or one relationship 
modelBuilder.Entity<UserSettings>() 
    .HasRequired(t => t.User) 
    .WithOptional(t => t.UserSettings);

This is not tested! Remove all the annotations from the entity classes. The link to Fluent API relationships in my comment above has more examples of the different kinds of relationship.

Answer 2

using anotations :

public class User
{
    [Key, Column("un")]
    public string Username { get; set; }
    public int Level { get; set; }
    //here is your foreign to UserSettings
    public int? UserSettingsID{ get; set; }

    [ForeignKey("UserSettingsID")] // not needed if you're using the '%ID' convention
    //Navigation property
    public virtual UserSettings UserSettings { get; set; }
}

public class UserSettings
{
    //UserSettings PK
    public int UserSettingsID{ get; set; }
    public int ActiveRefresh { get; set; }
}

I assume here that you don't need to retrieve the user from his settings