[Dbix-class] how to use a complex query in DBIx::Class

[Matt LeBlanc]

On 12/29/06, Jess Robinson <castaway at desert-island.demon.co.uk> wrote:
>
>
> On Tue, 26 Dec 2006, Matt LeBlanc wrote:
>
> > On 12/26/06, Jess Robinson <castaway at desert-island.demon.co.uk> wrote:
> >>  $schema->resultset('boards')->search({
> >>     'hiddenboards.userId' => 3,
> >>     'me.active' => 1,
> >>  }, {
> >>     'join' => 'hiddenboards',
> >>     '+select' => [ 'hiddenboards.userId' ],
> >>     '+as' => [ 'hidden' ],
> >>     'order_by' => [ 'pos' ],
> >>  })
> >>
> >>
> >>  .. and set up the relationship between board and hiddenboards to use an
> >>  inner join, not a left join.
> >>
> >>  I've not seen the syntax "SELECT .. hiddenboards.userId IS NOT NULL as
> >>  hidden" .. it's odd, why not use the proper join type?
> >>
> >>  Jess
> >
> > ... this isn't the same thing. He does not want all of the hidden
> > boards, as your change to an inner join would return. He wants all
> > boards with an extra field that tells him whether or not the board is
> > hidden (if the left join doesn't work, hiddenboards.boardId is null
> > and as such hidden is false).
> >
>
> Oh! That makes a lot more sense.. OTOH the JOIN .. ON ..
> hiddenboards.userId = 3 surely negates that effect?
>
> Jess
>

Sorry, I just realized I used the wrong field. Of course, this doesn't
matter as if the join condition fails, anything from hiddenboards is
null. Here is a full example of how this would work:

CREATE TABLE boards (
	id int,
	active int,
	pos int
	
);

INSERT INTO boards VALUES(1,1,1);
INSERT INTO boards VALUES(2,1,2);
INSERT INTO boards VALUES(3,1,3);

CREATE TABLE hiddenboards (
	userid int,
	boardId int	
);

INSERT INTO hiddenboards VALUES(1,1); -- not userid 3, so no join
INSERT INTO hiddenboards VALUES(3,2); -- userid 3, so valid join
-- no entry for id 3 so no join

SELECT boards.id,CASE WHEN hiddenboards.userid is not null THEN 1 ELSE
0 END AS hidden
FROM boards LEFT JOIN hiddenboards
ON hiddenboards.userid = 3
AND hiddenboards.boardid = boards.id
WHERE boards.active = 1
ORDER BY pos;

In this particular case, the rows returned are as follows:

id,hidden
1,0
2,1
3,0