I have a few questions...
Please assume that I'm not using and I can't use any ORM like
Transfer.
If your answer is "It depends", please specify what it depends on. :)
1. Should the parent object store the id of the child object, or a
reference to the actual child object?
Transfer needs us to always use reference to the child object, that's
why we can't say parent.setChildId(1). Instead, we must use
parent.setChild(transfer.get("child",1)), which I don't like.
However, if I only store the child ID, then I must force the user of
the parent object to always save the child object first, which is hard
to unit-test, which I don't like either.
2. If the child object is shared by more than 1 parent, should the
parent all reference to the same instance of the child object? If so,
how?
Possible implementation:
- Storing a struct of child objects by ID in Application scope? That
sounds bizarre and wrong
- Factory pattern with cache layer??
If not, then the updated child might be overwritten by an old child by
another parent object. e.g.
Parent A @ init'ed, has copy of Child1, Child1.name = "ONE"
Parent B @ init'ed, has another copy of Child1, Child1.name = "ONE"
Parent A update Child1's name to TWO
Parent A save (Child1 saved, Child1.name == TWO)
Parent B save (Child1 saved, Child1.name == ONE)
3. Should the parent act as facade and all operation goes through the
parent, when the child object is used only by the parent? Let say the
parent object is a Room object. The Room object has a Door object.
The Door has open() and close() method. If I need to close the door
of the room, what is the better?
room.getDoor().close() // no facade
room.closeDoor() // with room acts as facade
I like the 2nd one more, because the user of Room object does not need
to know about the Door object, but then wouldn't the Room object end
up having a lot of methods even though they're only one-liner?
Thank you very much guys~!
Henry Ho
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