From: Peter Rabbitson <ribasushi@cpan.org>
Date: Wed, 27 Oct 2010 10:18:41 +0000 (+0200)
Subject: Add undocumented ability to disable the join optimizer
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=ea95892eb6a71366db32b04137c7f2ee3b4ef841;p=dbsrgits%2FDBIx-Class-Historic.git

Add undocumented ability to disable the join optimizer

The capability system in its current form is insufficient - pending a
redesign/rewrite. In the meantime remove mention of it from Changes
and add an extra cap to disable the join-optimizer on request (prodded
by timbunce :)
---

diff --git a/Changes b/Changes
index ea01590..78a2a38 100644
--- a/Changes
+++ b/Changes
@@ -78,8 +78,6 @@ Revision history for DBIx::Class
           (first trigger instead of trigger for column)
 
     * Misc
-        - Refactored capability handling in Storage::DBI, allows for
-          standardized capability handling wrt query/enable/disable
         - Entire test suite now passes under DBIC_TRACE=1
         - Makefile.PL no longer imports GetOptions() to interoperate
           better with Catalyst installers
diff --git a/lib/DBIx/Class/Storage/DBI.pm b/lib/DBIx/Class/Storage/DBI.pm
index 29fc1bf..d07bb76 100644
--- a/lib/DBIx/Class/Storage/DBI.pm
+++ b/lib/DBIx/Class/Storage/DBI.pm
@@ -54,10 +54,13 @@ __PACKAGE__->mk_group_accessors('simple' => @storage_options);
 # will get the same rdbms version). _determine_supports_X does not need to
 # exist on a driver, as we ->can for it before calling.
 
-my @capabilities = (qw/insert_returning placeholders typeless_placeholders/);
+my @capabilities = (qw/insert_returning placeholders typeless_placeholders join_optimizer/);
 __PACKAGE__->mk_group_accessors( dbms_capability => map { "_supports_$_" } @capabilities );
-__PACKAGE__->mk_group_accessors( use_dbms_capability => map { "_use_$_" } @capabilities );
+__PACKAGE__->mk_group_accessors( use_dbms_capability => map { "_use_$_" } (@capabilities ) );
 
+# on by default, not strictly a capability (pending rewrite)
+__PACKAGE__->_use_join_optimizer (1);
+sub _determine_supports_join_optimizer { 1 };
 
 # Each of these methods need _determine_driver called before itself
 # in order to function reliably. This is a purely DRY optimization
diff --git a/lib/DBIx/Class/Storage/DBIHacks.pm b/lib/DBIx/Class/Storage/DBIHacks.pm
index 5256700..240fa3c 100644
--- a/lib/DBIx/Class/Storage/DBIHacks.pm
+++ b/lib/DBIx/Class/Storage/DBIHacks.pm
@@ -23,10 +23,11 @@ use namespace::clean;
 # {from} specs, aiding the RDBMS query optimizer
 #
 sub _prune_unused_joins {
-  my ($self) = shift;
-
+  my $self = shift;
   my ($from, $select, $where, $attrs) = @_;
 
+  return $from unless $self->_use_join_optimizer;
+
   if (ref $from ne 'ARRAY' || ref $from->[0] ne 'HASH' || ref $from->[1] ne 'ARRAY') {
     return $from;   # only standard {from} specs are supported
   }
@@ -100,31 +101,41 @@ sub _adjust_select_args_for_complex_prefetch {
     push @{$inner_attrs->{as}}, $attrs->{as}[$i];
   }
 
-  # construct the inner $from for the subquery
+  # construct the inner $from and lock it in a subquery
   # we need to prune first, because this will determine if we need a group_by below
   # the fake group_by is so that the pruner throws away all non-selecting, non-restricting
   # multijoins (since we def. do not care about those inside the subquery)
-  my $inner_from = $self->_prune_unused_joins ($from, $inner_select, $where, {
-    group_by => ['dummy'], %$inner_attrs,
-  });
-
-  # if a multi-type join was needed in the subquery - add a group_by to simulate the
-  # collapse in the subq
-  $inner_attrs->{group_by} ||= $inner_select
-    if first { ! $_->[0]{-is_single} } (@{$inner_from}[1 .. $#$inner_from]);
-
-  # generate the subquery
-  my $subq = $self->_select_args_to_query (
-    $inner_from,
-    $inner_select,
-    $where,
-    $inner_attrs,
-  );
 
-  my $subq_joinspec = {
-    -alias => $attrs->{alias},
-    -source_handle => $inner_from->[0]{-source_handle},
-    $attrs->{alias} => $subq,
+  my $subq_joinspec = do {
+
+    # must use it here regardless of user requests
+    local $self->{_use_join_optimizer} = 1;
+
+    my $inner_from = $self->_prune_unused_joins ($from, $inner_select, $where, {
+      group_by => ['dummy'], %$inner_attrs,
+    });
+
+    # if a multi-type join was needed in the subquery - add a group_by to simulate the
+    # collapse in the subq
+    $inner_attrs->{group_by} ||= $inner_select
+      if first { ! $_->[0]{-is_single} } (@{$inner_from}[1 .. $#$inner_from]);
+
+    # we already optimized $inner_from above
+    local $self->{_use_join_optimizer} = 0;
+
+    # generate the subquery
+    my $subq = $self->_select_args_to_query (
+      $inner_from,
+      $inner_select,
+      $where,
+      $inner_attrs,
+    );
+
+    +{
+      -alias => $attrs->{alias},
+      -source_handle => $inner_from->[0]{-source_handle},
+      $attrs->{alias} => $subq,
+    };
   };
 
   # Generate the outer from - this is relatively easy (really just replace
@@ -156,7 +167,7 @@ sub _adjust_select_args_for_complex_prefetch {
     }
   }
 
-  # scan the from spec against different attributes, and see which joins are needed
+  # scan the *remaining* from spec against different attributes, and see which joins are needed
   # in what role
   my $outer_aliastypes =
     $self->_resolve_aliastypes_from_select_args( $from, $outer_select, $where, $outer_attrs );
@@ -304,10 +315,10 @@ sub _resolve_aliastypes_from_select_args {
     );
   }
 
-  # mark all join parents as mentioned
+  # mark all restricting/selecting join parents as such
   # (e.g.  join => { cds => 'tracks' } - tracks will need to bring cds too )
-  for my $type (keys %$aliases_by_type) {
-    for my $alias (keys %{$aliases_by_type->{$type}}) {
+  for my $type (qw/restricting selecting/) {
+    for my $alias (keys %{$aliases_by_type->{$type}||{}}) {
       $aliases_by_type->{$type}{$_} = 1
         for (map { values %$_ } @{ $alias_list->{$alias}{-join_path} || [] });
     }