[odb-users] Many to many relationships - Insertion and deletion

[Nicolas ALBEZA]

Thanks a lot for your answer !

Regards,

2011/8/22 Boris Kolpackov <boris at codesynthesis.com>

> Hi Nicolas,
>
> Nicolas ALBEZA <n.albeza at gmail.com> writes:
>
> > I'm currently using ODB's many-to-many relationships in my projects, and
> i
> > was wondering how to insert and delete entires efficiently.
> >
> > My classes look like (most of it omitted for clarity):
> >
> > class Project
> > {
> > #pragma db value_not_null unordered
> >    list<lazy_shared_ptr<Account> > members;
> > }
> >
> > class Account
> > {
> >  #pragma db value_not_null inverse(members)
> > list<lazy_weak_ptr<Project> > projects;
> > }
> >
> > Currently, to add an Account to a Project, i'm doing something along the
> > lines of :
> >
> > shared_ptr<Account> account = db->find(...);
> > shared_ptr<Project> project = db->find(...);
>
> You don't really need to load the Account object (unless you need it
> later). Instead, you can create an "unloaded" lazy pointer:
>
> lazy_shared_ptr<Account> account (*db, account_id);
>
> The 'inverse' example uses this technique.
>
>
> > project->members.push_back(account);
> > db->update(project);
> >
> > Unfortunately, when looking at MySQL's query log, i can see the following
> > queries being executed :
> >
> > - A full update of the project entry
> > - Deletion of entries in the junction table
> > - And finally, insertion of an entry in the junction table
> >
> > The two first steps seem unnecessary, so i was wondering if there was a
> > better approach to do this.
>
> Unfortunately, I am afraid this is as efficient as it can get right
> now. We still need to work on the state change detection and more
> optimal container handling.
>
> If you had a one-to-many relationship, then making the 'many' side
> inverse (and thus getting rid of the container table) would have
> been a viable optimization.
>
> Boris
>



-- 
ALBEZA "Pause" Nicolas