如何在一对多关系EF 4.3.1中导航集合中删除后正确清理

Question

In a typical relation one to many, when I delete like:

var orderEntity = context.Orders.Single(o => o.orderID == entityID);
var baddetail = orderEntity.OrderDetails
                           .Single(od => od.orderDetailID == badOrderDetailID);
orderEntity.OrderDetails.Remove(baddetail);

I obtain the error:

The operation failed: The relationship could not be changed because one 
or more of the foreign-key properties is non-nullable. When a change is made 
to a relationship, the related foreign-key property is set to a null value. 
If the foreign-key does not support null values, a new relationship must 
be defined, the foreign-key property must be assigned another non-null value, 
or the unrelated object must be deleted.

As a solution was proposed to extend the DBContext.SaveChanges()

public override int SaveChanges()
    {

        foreach (OrderDetails od in this.OrderDetails.ToList())
        {
            // Remove OrderDetails without Order.
            if (od.Order == null)
            {
                this.OrderDetail.Remove(od);
            }
        }

        return base.SaveChanges();
    }

But is checking for OrderDetails with null Orders, when orderID is not nullable seem`s odd. How is the proper way of doing this ?

EDIT: As an example this odd deleting is happening when you expose through binding your Order.OrderDetails to and DataGrid.

Answer 1

You can just do this way:

var orderEntity = context.Orders.Single(o => o.orderID == entityID);
var baddetail = orderEntity.OrderDetails.Single(od => od.orderDetailID == badOrderDetailID);
context.OrderDetails.Remove(baddetail);

Because in your example you are not deleting entity. You are deleting relationship. So it tries to set null to your FK column and, of it is not nullable you will get and exception.

Answer 2

You are removing the OrderDetail from the Order's objects collection of OrderDetails. This is simply setting the OrderDetail's ID effectively to null and not marking it for deletion. This is not allowed as the FK from the OrderDetail to the Order table in the database is not nullable.

You should be doing

var orderEntity = context.Orders.Single(o => o.orderID == entityID);
var baddetail = orderEntity.OrderDetails
                       .Single(od => od.orderDetailID == badOrderDetailID);

context.OrderDetails.Remove(baddetail);