Question

my code like below

public class User
{
    public int ID { get; set; }
    public int BillingAddressID { get; set; }
    public Address BillingAddress { get; set; }
    public IList<Shipment> Shipments { get; set; }
}

public class Address
{
    public int ID { get; set; }
    public string Street { get; set; }
    public string City { get; set; }
    public string ZipCode { get; set; }
}

public class Shipment
{
    public int ID { get; set; }
    public string State { get; set; }
    public int DeliveryAddressID { get; set; }
    public Address DeliveryAddress { get; set; }
    public User ShipUser { get; set; }
    //[ForeignKey("ShipUser")]
    public int ShipUserID { get; set; }
    //public int UserId { get; set; }
}

public class TestContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Address> Addresses { get; set; }
    public DbSet<Shipment> Shipments { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Shipment>().HasRequired(u => u.ShipUser)
            .WithMany(d => d.Shipments)
            .HasForeignKey(c => c.ShipUserID)
            .WillCascadeOnDelete(false);
    }
}

1. if i remove the override method,i will get an error “SqlException: Introducing FOREIGN KEY constraint ‘FK_Shipments_Users_ShipUserID’ on table ‘Shipments’ may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
   Could not create constraint. See previous errors.”
2. if i remove ShipUserID in Shipment Class,it will work ok,when i see the table that is created by ef,i found a column named Shipment_UserID in table Shipment.I don`t know why.
3. if rename the class indenty key to UserID,it also work ok.

I try it anyway,but I don`t know the reason, I need some books about EF associations.

Answer 1

1. If you don’t have mapping specified without cascadeDelete=false for one relationship it will create multiple cascade paths if you have tow relationships to user from Shipment.
   By convention you can use public

   
Public User ShipUser { get; set; }
public int ShipUserID { get; set; }

it will use ShipUserID as foreign key by convention.

1. If you remove ShipUserID Ef need to create his own foreign key to keep the relationship . that is your ‘ Shipment_UserID’

2. rename the class indenty key to UserID I don’t understand what you meant.

Here is a good tutorial to start with