CoreData—为自动维护关系做了多少工作

tail和owningDog都由CoreData生成为retain属性。

2. 删除狗A(不删除狗B的新尾巴X)。

我一直在做这样的事情,为了清晰起见,我写了全文

-(void)graftThenKill
{
Tail* tempTail = A.tail;
A.tail = nil; // releases X, sets relationship to nil so we can delete without cascading
B.tail = tempTail; // retains X, sets Tail's owningDog to B
[moc deleteObject:A]; // now we have his tail, don't need A
}

-(void)graft
{
A.tail.owningDog = B; // Makes A's tail nil, safe to delete A without deleting X?
[moc deleteObject:A];
}