[Dbix-class] Unnecessary re-fetching via belongs_to relationships?

[Tim Watson]

Does $child have a parentid in its table to relate it to the parent ?

Couldn't you just use:

$child->parentid

Or do you want to use other values from the parent table in the loop?

-timw


On 6/28/06, Mark Blythe <list at markblythe.com> wrote:
> I have a situation where I see many seemingly needless queries
> happening.  This happens when I access a set of related child records
> via a has_many relationship, and then reference that original parent
> object via a belongs_to relationship from the children.  For each
> child object, the parent object is being re-fetched from the database,
> even though that child was originally fetched *through* the parent
> object.  For example (incomplete class examples):
>
> package MyApp::Schema::Main::Parent;
>
> __PACKAGE__->table('parent');
> __PACKAGE__->add_columns('parent_id');
> __PACKAGE__->set_primary_key('parent_id');
>
> __PACKAGE__->has_many(children => 'MyApp::Schema::Main::Child',
> 'parent_id');
>
>
> package MyApp::Schema::Main::Child;
>
>  __PACKAGE__->table('child');
>  __PACKAGE__->add_columns('child_id');
>  __PACKAGE__->set_primary_key('child_id');
>
>  __PACKAGE__->belongs_to(parent => 'MyApp::Schema::Main::Parent',
> 'parent_id');
>
> Now, somewhere else (via catalyst app):
>
> my $parent = $c->model('Main::Parent')->find($parent_id);
>
> foreach my $child ($parent->children()) {
>     print "child: ", $child->child_id, " parent: ",
> $child->parent->parent_id, "\n";
> }
>
> So every time through the loop, $child->parent->parent_id causes the
> parent record to be re-fetched from the database (according to DBIC
> debug output).
>
> Is this expected behavior?  I do have a few unusual areas in my DBIC
> setup which could be causing this issue, but I want to make sure this
> isn't normal before I launch a grand debugging mission.  It doesn't
> seem like it *should* be normal.
>
> BTW, I know I could get around it by simply accessing
> $parent->parent_id directly, but my real case is in some common
> display code where I don't always have the parent separately
> accessible.
>
> Thanks
>
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-- 
Tim Watson
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