Unable to determine the principal end of an association between the types [duplicate]

Answer 1

I think that you have to specify a ForeignKey relation on the Customer property that maps to the key property exists on the entity.

[Table("CUSTOMER_DETAIL")]
public class CustomerDetail
{
    [Required]
    [Column("CUSTOMER_DETAIL_ID")]
    public int Id {get; set;}
    // other fields

    [ForeignKey("Id")]
    public virtual Customer Customer {get; set;} 
}

This question refers to a different error, but has a similar goal to what you are trying to achieve.