سلام 

دو جدول دارم ApplicationUser , Customerمیخواهم به یکدیگر توسط توسط UserName متصل کنم ولی اتصال بین UserName و id جدول دیگری برقرار میشه و اررو میده. به چه صورت بنویسم ؟ 
ApplicationUser.cs

public class ApplicationUser : IdentityUser
    {
        public virtual Customer Customer { get; set; }
    }
}

Customer

 public Customer()
        {

        }
        [Key]
        public int Customer_Id { get; set; }
        public string  Name_Customer { get; set; }
        [ForeignKey("ApplicationUser")]
        public string UserName { get; set; }
        public virtual ApplicationUser ApplicationUser { get; set; }

 Error Migration
The relationship from 'Emp.Customer' to 'Customer.Emp' with foreign key properties {'UserName' : string} cannot target the primary key {'Customer_Id' : int} because it is not compatible. Configure a principal key or a set of compatible foreign key properties for this relationship.