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Re: correlated subqueries in DBIx::Class

by morgon (Priest)
on Jan 16, 2011 at 05:20 UTC ( #882510=note: print w/replies, xml ) Need Help??


in reply to correlated subqueries in DBIx::Class

I figured out my real problem, which is similar.

Instead of artists/cds/tracks I have customers/boxes/devices.

A customer has many boxes, a box has many devices.

I want to have a customer-resultset that contain a count-column of all devices that belong to a customer (via a box).

Here is what seems to do the trick, comments would be very welcome as this is the most complex thing I ever did with dbix::class:

my $crs = MyDBClass->resultset("Customer"); my $rs = $crs->search( undef, { "+select" => [ $crs->search( { "you.id" => { '=' => \'me.id' }}, { join => + { "boxes" => "devices" }, "+select" => ["devices.id"], +as =>["devic +e_id"], alias => 'you'})->count_rs->as_query, ], "+as" => [ "device_count" , ], } );
What may look as utter gibberish in fact generates the following SQL:

(SELECT me.id, me.bu_id, me.description, me.contact_name, me.contact_p +hone, me.contact_email, me.creation_ts, (SELECT COUNT( * ) FROM custo +mer you INNER JOIN box boxes ON boxes.customer_id = you.id INNER JOIN + device devices ON devices.box_id = boxes.id WHERE ( you.id = me.id ) +) FROM customer me)
I would like to stress that while this may look complex it actually is not too bad once you've wrapped your brain around the way DBIx::Class represents queries.

While this may not be the best demonstration of DBIx::Class strenghts I cannot recommend it high enough - while sometimes it may take some time figuring it out it saves tons of time in the long run.

If you don't use it already check it out.

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Re^2: correlated subqueries in DBIx::Class
by Anonymous Monk on Jan 20, 2014 at 00:00 UTC
    The "+as" of "device_count" does not exist in the generated SQL. Anyone have a solution????
      Sorry my error; the "+as" of "device_count" is not for the SQL but the resultant row in PERL. So device_count is a column name in each row.

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