Re: [eclipselink-users] @ManyToMany relationship for a List?

[cowwoc <cowwoc@xxxxxxxxxxxxxxxx>]

Sorry, I meant to say that "PlaylistItem has a ManyToOne to Video".

Gili


cowwoc wrote:
> 
> 
> I don't understand how "PlayListItem has a OneToOne to Video" would work.
> Each video can be associated with multiple playlists. As a consequence,
> each PlaylistItem would need to be associated with multiple videos as
> well. Shouldn't I do this instead?
> 
> Playlist has a OneToMany to PlaylistItem
> PlaylistItem has a OneToMany to Video
> PlaylistItem has its own identity
> 
> This would give you:
> 
> Playlist[id]
> Video[id]
> PlaylistItem[id, playlist_id, video_id]
> 
> What do you think?
> 
> Gili
> 
> 
> Tom Ware wrote:
>> 
>> Hi Gili,
>> 
>>    One workaround I can think of is to add another level of indirection.
>> 
>> i.e.
>> 
>> PlayList has a OneToMany to PlayListItem
>> PlayListItem has a OneToOne to Video
>> PlayListItem has its own identity.
>> 
>> You could even implement the mthods in PlayList to make PlayListItem
>> pretty much 
>> transparent to whoever was using your model.
>> 
>> -Tom
>> 
>> cowwoc wrote:
>>> BTW: Short-term, I would be quite happy to settle for a simple
>>> workaround
>>> than waiting for a fix, though if the fix is as simple to implement as I
>>> mentioned (dropping the primary key, adding an id) then I'd be even
>>> happier
>>> if you could implement it in the near future :)
>>> 
>>> This issue is very pressing for me right now because I don't see a
>>> simple
>>> workaround and my customer requires this feature (a single playlist to
>>> allow
>>> duplicate videos).
>>> 
>>> Gili
>>> 
>>> 
>>> cowwoc wrote:
>>>>
>>>> James Sutherland wrote:
>>>>> technically it is possible on a ManyToMany or when using a join table,
>>>>> but still rare for most models to want this.  I'm not certain what the
>>>>> JPA spec infers on duplicate support, but I assume it is either not
>>>>> supported, or not required, or more likely unspecified.
>>>>>
>>>> I think the spec implies it. Looking at sections 2.1.8.5.1 and
>>>> 2.1.8.5.2
>>>> compare the contents of "The following mapping defaults apply"
>>>> paragraphs.
>>>> You will notice that the last sentence of 2.1.8.5.1 requires a unique
>>>> key
>>>> constraint whereas 2.1.8.5.2 does not. I am asking precisely for this:
>>>> @ManyToMany should *not* enforce a unique constraint on pair of foreign
>>>> keys. Removing the primary key should be enough to satisfy this
>>>> requirement.
>>>>
>>>>
>>>> James Sutherland wrote:
>>>>> The main issue for relational is that things become tricky, i.e.
>>>>> insertion may work, but if you remove one of the duplicates, you now
>>>>> need
>>>>> to delete them all, then insert n-1 back.
>>>>>
>>>> I think you're making it more complicated than it needs to be. Instead
>>>> of
>>>> having a table with two foreign keys all you'd need is: [id, key1,
>>>> key2]
>>>> where id is the primary key. You then issue a query that returns the
>>>> first
>>>> row containing the values you'd like to delete, and delete it by its
>>>> id.
>>>>
>>> 
>>> Gili
>>> 
>>> 
>>> cowwoc wrote:
>>>> FYI, I filed a bug report for the original issue:
>>>> https://bugs.eclipse.org/bugs/show_bug.cgi?id=256978
>>>>
>>>> Gili
>>>>
>>>>
>>>> cowwoc wrote:
>>>>>
>>>>> Tim Hollosy wrote:
>>>>>> Anyway, on to your second question. Implementing indexed lists. What
>>>>>> do you mean implementing indexed lists on top of JPA?
>>>>>>
>>>>>> java.util.List is already indexed..so I don't really follow your
>>>>>> question.
>>>>>>
>>>>> JPA 1.0 does not retain the element index. The best you can do is
>>>>> @OrderBy. If the order is arbitrary (chosen by the end-user) you need
>>>>> to
>>>>> rely in ordering by indexes but currently JPA will not manage indexes
>>>>> for
>>>>> you under the hood. For example, if you want to insert an element
>>>>> between
>>>>> two other elements you will need to update the indexes of all elements
>>>>> that allow, etc.
>>>>>
>>>>> Gili
>>>>>
>>>>
>>> 
>>> 
>>> 
>>> 
>>> 
>> _______________________________________________
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>> eclipselink-users@xxxxxxxxxxx
>> https://dev.eclipse.org/mailman/listinfo/eclipselink-users
>> 
>> 
> 
> 

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