From: Peter Rabbitson Date: Mon, 21 Sep 2009 10:49:30 +0000 (+0000) Subject: Undocument the from attribute (the description was mostly outdated anyway) X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=f4342a8c9f90d8a5526c22bfcbeb17631242b404;p=dbsrgits%2FDBIx-Class-Historic.git Undocument the from attribute (the description was mostly outdated anyway) --- diff --git a/lib/DBIx/Class/ResultSet.pm b/lib/DBIx/Class/ResultSet.pm index 78fd277..45e838f 100644 --- a/lib/DBIx/Class/ResultSet.pm +++ b/lib/DBIx/Class/ResultSet.pm @@ -3575,177 +3575,6 @@ By default, searches are not cached. For more examples of using these attributes, see L. -=head2 from - -=over 4 - -=item Value: \@from_clause - -=back - -The C attribute gives you manual control over the C clause of SQL -statements generated by L, allowing you to express custom C -clauses. - -NOTE: Use this on your own risk. This allows you to shoot off your foot! - -C will usually do what you need and it is strongly recommended that you -avoid using C unless you cannot achieve the desired result using C. -And we really do mean "cannot", not just tried and failed. Attempting to use -this because you're having problems with C is like trying to use x86 -ASM because you've got a syntax error in your C. Trust us on this. - -Now, if you're still really, really sure you need to use this (and if you're -not 100% sure, ask the mailing list first), here's an explanation of how this -works. - -The syntax is as follows - - - [ - { => }, - [ - { => , -join_type => 'inner|left|right' }, - [], # nested JOIN (optional) - { => , ... (more conditions) }, - ], - # More of the above [ ] may follow for additional joins - ] - - - JOIN - - [JOIN ...] - ON = - - -An easy way to follow the examples below is to remember the following: - - Anything inside "[]" is a JOIN - Anything inside "{}" is a condition for the enclosing JOIN - -The following examples utilize a "person" table in a family tree application. -In order to express parent->child relationships, this table is self-joined: - - # Person->belongs_to('father' => 'Person'); - # Person->belongs_to('mother' => 'Person'); - -C can be used to nest joins. Here we return all children with a father, -then search against all mothers of those children: - - $rs = $schema->resultset('Person')->search( - undef, - { - alias => 'mother', # alias columns in accordance with "from" - from => [ - { mother => 'person' }, - [ - [ - { child => 'person' }, - [ - { father => 'person' }, - { 'father.person_id' => 'child.father_id' } - ] - ], - { 'mother.person_id' => 'child.mother_id' } - ], - ] - }, - ); - - # Equivalent SQL: - # SELECT mother.* FROM person mother - # JOIN ( - # person child - # JOIN person father - # ON ( father.person_id = child.father_id ) - # ) - # ON ( mother.person_id = child.mother_id ) - -The type of any join can be controlled manually. To search against only people -with a father in the person table, we could explicitly use C: - - $rs = $schema->resultset('Person')->search( - undef, - { - alias => 'child', # alias columns in accordance with "from" - from => [ - { child => 'person' }, - [ - { father => 'person', -join_type => 'inner' }, - { 'father.id' => 'child.father_id' } - ], - ] - }, - ); - - # Equivalent SQL: - # SELECT child.* FROM person child - # INNER JOIN person father ON child.father_id = father.id - -You can select from a subquery by passing a resultset to from as follows. - - $schema->resultset('Artist')->search( - undef, - { alias => 'artist2', - from => [ { artist2 => $artist_rs->as_query } ], - } ); - - # and you'll get sql like this.. - # SELECT artist2.artistid, artist2.name, artist2.rank, artist2.charfield FROM - # ( SELECT me.artistid, me.name, me.rank, me.charfield FROM artists me ) artist2 - -If you need to express really complex joins, you -can supply literal SQL to C via a scalar reference. In this case -the contents of the scalar will replace the table name associated with the -resultsource. - -WARNING: This technique might very well not work as expected on chained -searches - you have been warned. - - # Assuming the Event resultsource is defined as: - - MySchema::Event->add_columns ( - sequence => { - data_type => 'INT', - is_auto_increment => 1, - }, - location => { - data_type => 'INT', - }, - type => { - data_type => 'INT', - }, - ); - MySchema::Event->set_primary_key ('sequence'); - - # This will get back the latest event for every location. The column - # selector is still provided by DBIC, all we do is add a JOIN/WHERE - # combo to limit the resultset - - $rs = $schema->resultset('Event'); - $table = $rs->result_source->name; - $latest = $rs->search ( - undef, - { from => \ " - (SELECT e1.* FROM $table e1 - JOIN $table e2 - ON e1.location = e2.location - AND e1.sequence < e2.sequence - WHERE e2.sequence is NULL - ) me", - }, - ); - - # Equivalent SQL (with the DBIC chunks added): - - SELECT me.sequence, me.location, me.type FROM - (SELECT e1.* FROM events e1 - JOIN events e2 - ON e1.location = e2.location - AND e1.sequence < e2.sequence - WHERE e2.sequence is NULL - ) me; - =head2 for =over 4