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

[Tom Ware <tom.ware@xxxxxxxxxx>]

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