X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FStorage%2FDBIHacks.pm;fp=lib%2FDBIx%2FClass%2FStorage%2FDBIHacks.pm;h=ec6a32f779ec45e0f66766b7c119c926759f4679;hb=656524408f86cf27df8c70a900f452421be9c4e4;hp=3f3662bcb9e509edd3a0aa428e34306f01687607;hpb=2268474f6427676f69515a0ea47d638eaa6b497c;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Storage/DBIHacks.pm b/lib/DBIx/Class/Storage/DBIHacks.pm
index 3f3662b..ec6a32f 100644
--- a/lib/DBIx/Class/Storage/DBIHacks.pm
+++ b/lib/DBIx/Class/Storage/DBIHacks.pm
@@ -681,11 +681,12 @@ sub _extract_order_criteria {
 }
 
 sub _order_by_is_stable {
-  my ($self, $ident, $order_by) = @_;
+  my ($self, $ident, $order_by, $where) = @_;
 
-  my $colinfo = $self->_resolve_column_info(
-    $ident, [ map { $_->[0] } $self->_extract_order_criteria($order_by) ]
-  );
+  my $colinfo = $self->_resolve_column_info($ident, [
+    (map { $_->[0] } $self->_extract_order_criteria($order_by)),
+    $where ? @{$self->_extract_fixed_condition_columns($where)} :(),
+  ]);
 
   return undef unless keys %$colinfo;
 
@@ -700,4 +701,41 @@ sub _order_by_is_stable {
   return undef;
 }
 
+# returns an arrayref of column names which *definitely* have som
+# sort of non-nullable equality requested in the given condition
+# specification. This is used to figure out if a resultset is
+# constrained to a column which is part of a unique constraint,
+# which in turn allows us to better predict how ordering will behave
+# etc.
+#
+# this is a rudimentary, incomplete, and error-prone extractor
+# however this is OK - it is conservative, and if we can not find
+# something that is in fact there - the stack will recover gracefully
+# Also - DQ and the mst it rode in on will save us all RSN!!!
+sub _extract_fixed_condition_columns {
+  my ($self, $where, $nested) = @_;
+
+  return unless ref $where eq 'HASH';
+
+  my @cols;
+  for my $lhs (keys %$where) {
+    if ($lhs =~ /^\-and$/i) {
+      push @cols, ref $where->{$lhs} eq 'ARRAY'
+        ? ( map { $self->_extract_fixed_condition_columns($_, 1) } @{$where->{$lhs}} )
+        : $self->_extract_fixed_condition_columns($where->{$lhs}, 1)
+      ;
+    }
+    elsif ($lhs !~ /^\-/) {
+      my $val = $where->{$lhs};
+
+      push @cols, $lhs if (defined $val and (
+        ! ref $val
+          or
+        (ref $val eq 'HASH' and keys %$val == 1 and defined $val->{'='})
+      ));
+    }
+  }
+  return $nested ? @cols : \@cols;
+}
+
 1;