Why Deferred Deletion does not use the GCRecord field to store a parent object when deleting child objects

Hello Frank,

Please note that XPO classes can have more than one parent property. For example:

C#
public class Product : XPObject {
    public Product(Session session) : base(session) {}

    Supplier fSupplier;
    public Supplier Supplier {
        get => fSupplier;
        set => SetPropertyValue(nameof(Supplier), ref fSupplier, value);
    }

    Category fCategory;
    public Category Category {
        get => fCategory;
        set => SetPropertyValue(nameof(Category), ref fCategory, value);
    }
}

We do not store references to parent objects anywhere because we did not intend the Deferred Deletion feature to support restoring deleted records.

As for the GCRecord field, it is not the right place to store old references. We set the GCRecord field to a random value to allow using unique constraints when the Deferred Deletion feature is enabled.

The following example demonstrates a problem with unique constraints and Deferred Deletion:

1. Create a Category table with the CategoryName column that has a unique constraint.
2. Insert a "Category A" category.
3. Delete the "Category A" category using the Deferred Deletion feature.
4. Now you cannot insert another "Category A" category unless you physically delete the previous category from the database.

The solution to this problem is adding the GCRecord field to a unique index.