On Fri, 23 Mar 2007, John Siracusa wrote:
> If you add the same bar twice, it'll add a new mapping each time.
> That's what add_bars() does.
Given that Rose knows that this is a many-to-many relationship between
foos and bars, isn't it pretty far-fetched that you would actually
want duplicate records in the mapping table?
> If you try to do what Jud suggested:
>
> On 3/11/07, Jud <[EMAIL PROTECTED]> wrote:
> > You could add a UNIQUE INDEX(foo_id, bar_id)
>
> All that'll do is die with an error when you try to add the second
> one. If what you really want to do is "add a related bar only if that
> bar is not already related" then you have to write that out, rather
> than simply calling add_bars() multiple times with the same argument.
> In your example, it'd be something like:
>
> unless(grep { $_->string eq 'I am Bar' } $foo->bars)
> {
> $foo->add_bars({ string => "I am Bar" });
> }
That would work, but $foo->bars() could potentially return a lot
of relationships, and in this case I'm only interested in a single
one to check if it exists or not.
Another approach would be to 1) select the record from bars and 2)
select the record from the mapping table, which would be faster in case
there's many bars for a given foo.
Or, you could join the mapping table and the bars table to figure it
out with a single select.
In a 1:1 relationship, if you do
$foo->bar({ string => "I am Bar" });
and the bars record doesn't exist yet, Rose does
SELECT bar_id, id, string FROM foos WHERE string = ? - bind params: I am Foo
SELECT id, string FROM bars WHERE string = ? - bind params: I am Bar
INSERT INTO bars
( id, string) VALUES ( ?, ?) - bind params: , I am Bar
INSERT INTO foos
( bar_id, id, string) VALUES ( ?, ?, ?) - bind params: 1, , I am Foo
If the bars record exists, however, Rose does
SELECT bar_id, id, string FROM foos WHERE string = ? - bind params: I am Foo
SELECT id, string FROM bars WHERE string = ? - bind params: I am Bar
UPDATE foos SET bar_id = ?, string = ?
WHERE id = ? - bind params: 1, I am Foo, 1
which is exactly the right thing to do.
Could something along these lines be added to the many-to-many
relationship handling?
-- Mike
Mike Schilli
[EMAIL PROTECTED]
>
> -John
>
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