[odb-users] polymorphic base orphans

[Сергей Никонов]

Hi everybody,
 
I encountered a problem concerned with appearing «orphan» records in the database representing base entities of a polymorphic hierarchy. An example below demonstrates the issue. There are a polymorphic abstract base class with two derived classes one of which contains a pointer to another.
 
#pragma db object abstract polymorphic
struct base
{
  virtual ~base() {}
#pragma db id auto
  int id;
};
#pragma db object
struct derived1
  : public base
{
#pragma db null
  int value;
};
#pragma db object
struct derived2
  : public base
{
#pragma db null
  int value;
#pragma db null on_delete(cascade)
  std::shared_ptr<derived1> ref;
};
 
After persisting objects like this:
 
    auto d1 = std::make_shared<derived1>();
    db.persist(d1);
    auto d2 = std::make_shared<derived2>();
    d2->ref = d1;
    db.persist(d2);
 
lets delete «d1» instance:
 
    db.erase<base>(d1->id);
 
After committing the database will contain an orphan record:
   id    typeid
   ----------------
   2    derived2
 
When I try to resolve the issue by manually deleting «base» instance in a database trigger I receive an exception from ODB.
Is there any reasonable way how to deal with this (quite typical in my opinion) situation in general?
 
Thank you in advance,
Sergey