One other thing to note is that Model.merge actually creates a managed copy
of whatever it merges. The original object you pass to it is left completely
unchanged. So if you do
def doSomething(student : Student) = {
Model.merge(student)
student.courses.add(...)
student.balance += 1000000
}
None of those changes will show up since you're not working on the managed
copy. What you would really want to do is something like
def doSomething(student : Student) = {
val merged = Model.merge(student)
merged.courses.add(...)
merged.balance += 1000000
}
Derek
On Mon, Sep 29, 2008 at 7:48 AM, Derek Chen-Becker <[EMAIL PROTECTED]>wrote:
> Argh! Stupid gmail hotkeys... Here's what I wanted to say:
>
> class Student {
> // ... everything else up here ...
>
> @ManyToMany{ val targetEntity = classOf[Course] }
> var courses : java.util.Set[Course] = new java.util.HashSet[Course]
> }
>
> class Course {
> // ... everything else up here ...
>
> @ManyToMany { val targetEntity = classOf[Student], val mappedBy =
> "courses" }
> var students : java.util.Set[Student] = new java.util.HashSet[Student]
> }
>
> Since the student is the owning side, if you want to delete the
> relationship you need to do it from the student:
>
> def unenroll (student : Student, course : Course ) =
> student.courses.remove(course)
>
> this assumes that student and course are both managed in the EM session
> already. If neither is, you could do
>
> def unenroll (student : Student, course : Course) = {
> student.courses.remove(course)
> Model.merge(student)
> }
>
> The big thing to remember is that none of these operations actually do
> anything to the database unless they happen within a transaction. In the
> demo code I've put up this should happen automatically. Having said all of
> this, what issue are you running into?
>
> Derek
>
>
>
> On Mon, Sep 29, 2008 at 7:35 AM, Derek Chen-Becker <[EMAIL PROTECTED]>wrote:
>
>> With many to many you still have an "owning" side that's responsible for
>> things. For instance, given the following classes:
>>
>> class Student {
>>
>>
>>
>> On Mon, Sep 29, 2008 at 6:17 AM, Tim Perrett <[EMAIL PROTECTED]>wrote:
>>
>>>
>>> Hey Guys,
>>>
>>> Im having a few problems doing a many-to-many deletion using JPA...
>>> can anyone point me in the right direction?
>>>
>>> Thanks
>>>
>>> Tim
>>> >>>
>>>
>>
>
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