Entity Framework: How do I delete table rows that reference each other?

Question

How do I delete the order without getting this exception?

UserLicenses references SerialOnOrderDetails and vice-versa:

The DELETE statement conflicted with the REFERENCE constraint "FK_SerialsOnOrderDetail_UserLicenses". The conflict occurred in database "sales", table "dbo.SerialsOnOrderDetail", column 'UserLicenseId'.

Delete confirmed controller action code:

[Authorize(Roles = "admin")]    
[HttpPost, ActionName("Delete")]
public async Task<ActionResult> DeleteConfirmed(int id)
{
    Order order = GetOrderById(id);

    if (order.UserLicenses.Count > 0)
    {
        context.UserLicenses.RemoveRange(order.UserLicenses);
    }

    if (order.SerialsOnOrderDetails.Count > 0)
    {
        context.SerialsOnOrderDetails.RemoveRange(order.SerialsOnOrderDetails);
    }

    context.Orders.Remove(order);

    context.SaveChanges(); // Exception here !!!
}

Additional classes:

public partial class UserLicense
{   
    public string Id { get; set; }
    public int OrderId { get; set; }
    public string ProductId { get; set; }
    public int CustomerId { get; set; }
    public string AssignedUserId { get; set; }
    public bool IsActive { get; set; }

    public virtual AspNetUser AspNetUser { get; set; }
    public virtual Customer Customer { get; set; }
    public virtual Order Order { get; set; }
    public virtual Product Product { get; set; }

    public virtual ICollection<SerialsOnOrderDetail> SerialsOnOrderDetails { get; set; }
}

public partial class SerialsOnOrderDetail
{
   public int orderID { get; set; }
   public string serial { get; set; }
   public string productID { get; set; }
   public string UserLicenseId { get; set; }
   public int customerID { get; set; }

   public virtual Product Product { get; set; }
   public virtual Serial Serial1 { get; set; }
   public virtual Order Order { get; set; }
   public virtual UserLicense UserLicense { get; set; }
   public virtual Customer Customer { get; set; }
}

public partial class Order
{
    public Order()
    {
        this.OrderDetails = new HashSet<OrderDetail>();
        this.SerialsOnOrderDetails = new HashSet<SerialsOnOrderDetail>();
        this.UserLicenses = new HashSet<UserLicense>();
    }

    public int orderID { get; set; }
    public int customerID { get; set; }
    public string promoCodeID { get; set; }
    public System.DateTime date { get; set; }
    public Nullable<int> resellerID { get; set; }
    public string invoiceID { get; set; }
    public string poNumber { get; set; }
    public Nullable<System.DateTime> paymentDate { get; set; }
    public Nullable<bool> validated { get; set; }
    public string resellerOrderID { get; set; }
    public Nullable<int> parentOrderID { get; set; }
    public int months { get; set; }

    public virtual Customer Customer { get; set; }
    public virtual ICollection<OrderDetail> OrderDetails { get; set; }
    public virtual PromoCode PromoCode { get; set; }
    public virtual Reseller Reseller { get; set; }
    public virtual ICollection<SerialsOnOrderDetail> SerialsOnOrderDetails { get; set; }
    public virtual Order ParentOrder { get; set; }
    public virtual ICollection<UserLicense> UserLicenses { get; set; }
}

Answer 1

Did you verify if UserLicenses and SerialsOnOrderDetails collections are properly loaded and not empty? Are you sure removerange is the proper way to do it? I suggest you to read a few tutorials about EF if you are not used to it.

Maybe you'll have to update GetOrderById with.Include("....") directives to load these collections, or load the related items manually.

Answer 2

That constraint message you quote is from the underlying SQL Server. It's not an EF error as such, it's passed through.

When I get this sort of problem in TSQL the solution is generally to delete both of the mutually referencing rows in a single transaction.

While I'm not terribly familiar with EF, a quick search turn up this example of putting multiple operations into a single transactional context instead of the default behaviour of a single transaction per operation.

{
    context.Database.Log = Console.WriteLine;
    using (DbContextTransaction transaction = context.Database.BeginTransaction())
    {
        try
        {
            Author author1 = new Author() {    Name = "Mark" };
            Author author2 = new Author() {    Name = "John" };
            
            context.Authors.Add(author1);
            context.SaveChanges();
            
            context.Authors.Add(author2);
            context.SaveChanges();
            transaction.Commit();
        }
        catch (Exception ex)
        {
            transaction.Rollback();
        }
    }
}

I notice another respondent describes other things that could be wrong. It is entirely possible that we are both right and there are multiple issues to resolve.