Re: circular references and ORM
Lew wrote:
Daniel Pitts wrote:
In particular for JPA and Hibernate using annotations, you have a
@OneToMany(targetEntity=Monkey.class) Set<Monkey> monkeys; in the
Barrel, and a @ManyToOne Barrel barrel; in the Monkey class.
What's important to remember in Relational theory is that ALL
relations include two endpoints, whether you model that explicitly or
not.
I have trouble remembering who "owns" the relation, so that the other
one can say "mappedBy" in its annotation. Monkey owns the Monkey-Barrel
connection, right? Something like
@OneToMany( targetEntity=Monkey.class, mappedBy="barrel" )
Set <Monkey> monkeys;
?
You *can* do that (and often it makes sense). I believe there is also a
way to have a third table that is just for the relation, something like
Monkey_Barrel (id, Monkey_Id, Barrel_id). Which might make more sense
if semantically neither monkey nor barrel should "own" the reference.
Ofcourse, this does have performance implications :-p
--
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