Rob Kinyon wrote:
On Mon, Jun 29, 2009 at 10:13, Peter Rabbitson<[email protected]> wrote:
A classical use-case is "right side condition on a left-join". There is
no way to emulate those appropriately with WHERE - the condition has to
reside in the join spec itself: i.e. you need to get ALL artists, and
all cds issued in a *specific year*. If you do a regular join - you get
only artists with CDs. If you do a (standard for has_many) left join -
you populate the right side of the join with CDs you don't want, and there
is no way to WHERE them out.
I'm not seeing this. Code, please?
I want to help because this is a CRITICAL FEATURE, as far as I'm
concerned. I have to jump through hoops and repetitive queries within
dbix-class to get my permissions data structure to resolve answers
because of this lack... It constrains my application because I can't
execute the same queries I would otherwise.
In advanced query creation, there are data sets that you cannot declare
without using subqueries or multiple conditions in a join.
I can't show you code that does what he asks because it is impossible
for DBIx::Class to describe that relationship.
"Give me data on artists who didn't release a cd in 1994"
The SQL would be like
select artists.* from artists LEFT JOIN cds ON (cds.artist =
artists.artist AND cd.year = 1994) WHERE cd.year IS NULL;
You can't do any other query (than utilizing a subquery to limit the
joined set) to describe the same data set. Can you think of one that
you can declare in DBIx-Class without hacking in a subquery?
David
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