On 11/7/06, Jud Dagnall <[EMAIL PROTECTED]> wrote:
> In my application, there is are projects, tags, and profiles (users).
> Projects can be tagged by multiple profiles. Each tag has a many-to-many
> relationship both projects and profiles. There's a mapping table
> (tag_project_profile_map) with a 3-column primary key that relates those
> three tables.
> [...]
> I'd like to be able to add tags to a project as follows (specifying the
> missing primary key value):
>
> $project->tags( { name = 'cool_stuff', profile_id => 1 } );
> $project->save;
>
> However, this gives me an error because the 'tags' table doesn't
> actually have a profile_id, only the mapping table does.
There are a few possible ways to go about this. One is the manual
way, where you actually instantiate and them modify the map record
separately, as shown here:
> my $mapping = TagProjectProfileMap->new(
> {project_id => 1,
> tag_id => 2,
> profile_id => 3});
> $mapping->save;
(Although the argument to new() should not be a hashref.)
Another way is to set the tags, use the Manager to re-fetch them,
modify the map records, and then re-save them:
$project->new(id => 1)->load;
$project->tags(...);
$project->save;
$project =
Project::Manager->get_prouducts(
with_objects => [ 'tags' ],
with_map_records => 1,
query => [ id => 1 ])->[0];
foreach my $tag ($project->tags)
{
$tag->map_record->profile_id(...);
$tag->map_record->save;
}
That's a save(), load(), and then re-save() for each map record, however.
The next method I can think of is to split up your single mapping
table into two mapping tables, e.g.. project_tag_map table and a
project_profile_map. Then you could just do:
$project->tags(...);
$project->profiles(...);
$project->save;
Maybe that's not exactly in keeping with what you're trying to model,
but the three-way tag_project_profile_map mapping table is a bit odd.
The concept of a map table in RDBO is supposed to be part of a
many-to-many relationship between two classes, not three. As you've
discovered, it'll pretty much still work with three, but there's a bit
of a mismatch in intent.
Finally, you could forego the many-to-many relationship definition and
instead (or "also") defined it as chain of relationships that
explicitly includes the mapping table:
Project
|
one to many <- rel name: tag_profile_map_records
|
v
TagProjectProfileMap
/ \
foreign key foreign key
/ \
v v
Tag Profile
Then do:
$project->new(id => 1)->load;
$project->tag_profile_map_records
(
{
tag => { name => 'foo', ... },
profile => { username => 'bar', ... },
},
{
tag => { name => 'baz', ... },
profile => { username => 'blee', ... },
},
...
);
$project->save;
> I looked at trying define a custom primary_key_generator() function in
> my TagProjectProfileMap, but I didn't see that I could get the
> additional parameters.
A pk generator is definitely not the right approach to this problem.
-John
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