say i have a persistent parent class, Employee, with a collection of
child objects, PhoneNumber:
@PersistenceCapable(identityType = IdentityType.APPLICATION)
class Employee implements Serializable
{
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
Long id;
@Persistent(mappedBy = "employee")
List<PhoneNumber> phoneNumbers;
}
@PersistenceCapable(identityType = IdentityType.APPLICATION)
class PhoneNumber implements Serializable
{
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
Key key;
@Persistent(mappedBy = "phoneNumbers")
Employee employee;
@Persistent
Integer phoneNumber;
}
when deleting all child objects (PhoneNumber), there are two possible
ways to do this:
(1) set the collection of child objects on the parent object to an
empty collection (or null):
static void deletePhoneNumbers( Long p_employeeId, PersistentManager
p_manager )
{
Employee l_employee = p_manager.getObjectById( Employee.class,
p_employeeId );
l_employee.phoneNumbers = new ArrayList<PhoneNumber>();
p_manager.makePersistent( l_employee );
}
or
(2) delete all child objects belonging to the parent object:
static void deletePhoneNumbers( Employee p_employee,
PersistenceManager p_manager )
{
Query l_query = p_manager.newQuery( PhoneNumber.class );
l_query.setFilter( "employee == p_employee" );
l_query.declareParameters( "Employee p_employee" );
l_query.deletePersistentAll( p_employee );
}
both ways seem to have the same effect. as one might expect, the
collection of child objects in the parent array are removed and the
child objects themselves are removed from the data store.
my question is:
as far as hits on the data store (and the quota/fees associated with
those hits) are concerned, which incurs a greater number of calls
against the datastore (and, subsequently, incurs more fees)?
when you look at what's happening in the low-level API, do both ways
of deleting child objects result in the same number of calls against
the data store or is one way less costly than the other?
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