Question

I can’t figure out why this is causing EF error: Invalid column name ‘User_UserId’ when saving in EF.

Here is my model:

 [DataContract(IsReference = true)]
public class User
{
    [Key]
    [DataMember]
    public virtual Guid UserId { get; set; }

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

    [DataMember]
    public virtual string Password { get; set; }

    [DataMember]
    public virtual string Email { get; set; }

    [DataMember]
    public virtual ICollection<FriendList> FriendLists { get; set; }
}

[DataContract(IsReference = true)]
public class FriendList
{
    [Key]
    [DataMember]
    public virtual Guid FriendListId { get; set; }

    [DataMember]
    [ForeignKey("User")]
    public virtual Guid UserId { get; set; }

    [DataMember]
    public virtual User User { get; set; }

    [DataMember]
    [ForeignKey("FriendUser")]
    public virtual Guid FriendUserId { get; set; }

    [DataMember]
    public virtual User FriendUser { get; set; }
}

basically, its one to many relationship with users having a friendlists.

Answer 1

You have two navigation properties of type User in your FriendList class. EF cannot figure out which of these belong to User.FriendLists and then creates for all three navigation properties a separate one-to-many relationship, one of them has the default foreign key name User_UserId.

You can overwrite this convention with the InverseProperty attribute:

public class FriendList
{
    // ...

    [DataMember]
    [InverseProperty("FriendLists")]
    public virtual User User { get; set; }

    // ...
}

Now, User.FriendLists and FriendList.User are the endpoints of the same one-to-many relationship and FriendList.FriendUser defines a second one-to-many relationship (but without an endpoint in the User class).