X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FStorage%2FDBI%2FMSSQL.pm;h=fedec7fa423533f1b36c0e65a3d61ee765b92f96;hb=0777ad33930b2c09258f9752e4e76c27ca75f347;hp=be1c3992a3d56d5078c5a62e31ea1884ff42dc2f;hpb=2dde7fb770ab920c186ed18db544f6e76f90c8b3;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Storage/DBI/MSSQL.pm b/lib/DBIx/Class/Storage/DBI/MSSQL.pm
index be1c399..fedec7f 100644
--- a/lib/DBIx/Class/Storage/DBI/MSSQL.pm
+++ b/lib/DBIx/Class/Storage/DBI/MSSQL.pm
@@ -3,7 +3,7 @@ package DBIx::Class::Storage::DBI::MSSQL;
 use strict;
 use warnings;
 
-use base qw/DBIx::Class::Storage::DBI::AmbiguousGlob DBIx::Class::Storage::DBI/;
+use base qw/DBIx::Class::Storage::DBI/;
 use mro 'c3';
 
 use List::Util();
@@ -179,8 +179,9 @@ sub _execute {
 sub last_insert_id { shift->_identity }
 
 #
-# MSSQL is retarded wrt ordered subselects. One needs to add a TOP 100%
-# to *all* subqueries, do it here.
+# MSSQL is retarded wrt ordered subselects. One needs to add a TOP
+# to *all* subqueries, but one also can't use TOP 100 PERCENT
+# http://sqladvice.com/forums/permalink/18496/22931/ShowThread.aspx#22931
 #
 sub _select_args_to_query {
   my $self = shift;
@@ -189,8 +190,12 @@ sub _select_args_to_query {
 
   # see if this is an ordered subquery
   my $attrs = $_[3];
-  if ( scalar $self->sql_maker->_order_by_chunks ($attrs->{order_by}) ) {
-    $sql =~ s/^ \s* SELECT \s/SELECT TOP 100 PERCENT /xi;
+  if ( scalar $self->_parse_order_by ($attrs->{order_by}) ) {
+    $self->throw_exception(
+      'An ordered subselect encountered - this is not safe! Please see "Ordered Subselects" in DBIx::Class::Storage::DBI::MSSQL
+    ') unless $attrs->{unsafe_subselect_ok};
+    my $max = 2 ** 32;
+    $sql =~ s/^ \s* SELECT \s/SELECT TOP $max /xi;
   }
 
   return wantarray
@@ -235,23 +240,27 @@ sub _get_mssql_version {
   if ($data->{Character_Value} =~ /^(\d+)\./) {
     return $1;
   } else {
-    $self->throw_exception(q{your MSSQL server doesn't have a version!});
+    $self->throw_exception(q{Your ProductVersion's Character_Value is missing or malformed!});
   }
 }
 
-sub _sql_maker_opts {
-  my ( $self, $opts ) = @_;
+sub sql_maker {
+  my $self = shift;
 
-  if ( $opts ) {
-    $self->{_sql_maker_opts} = { %$opts };
-  }
+  unless ($self->_sql_maker) {
+    unless ($self->{_sql_maker_opts}{limit_dialect}) {
+      my $version = eval { $self->_get_mssql_version; } || 0;
+
+      $self->{_sql_maker_opts} = {
+        limit_dialect => ($version >= 9 ? 'RowNumberOver' : 'Top'),
+        %{$self->{_sql_maker_opts}||{}}
+      };
+    }
 
-  my $version = $self->_get_mssql_version;
+    my $maker = $self->next::method (@_);
+  }
 
-  return {
-    limit_dialect => ($version >= 9 ? 'RowNumberOver' : 'Top'),
-    %{$self->{_sql_maker_opts}||{}}
-  };
+  return $self->_sql_maker;
 }
 
 1;
@@ -299,6 +308,54 @@ $table_name ON>. Unfortunately this operation in MSSQL requires the
 C<db_ddladmin> privilege, which is normally not included in the standard
 write-permissions.
 
+=head2 Ordered Subselects
+
+If you attempted the following query (among many others) in Microsoft SQL
+Server
+
+ $rs->search ({}, {
+  prefetch => 'relation',
+  rows => 2,
+  offset => 3,
+ });
+
+You may be surprised to receive an exception. The reason for this is a quirk
+in the MSSQL engine itself, and sadly doesn't have a sensible workaround due
+to the way DBIC is built. DBIC can do truly wonderful things with the aid of
+subselects, and does so automatically when necessary. The list of situations
+when a subselect is necessary is long and still changes often, so it can not
+be exhaustively enumerated here. The general rule of thumb is a joined
+L<has_many|DBIx::Class::Relationship/has_many> relationship with limit/group
+applied to the left part of the join.
+
+In its "pursuit of standards" Microsft SQL Server goes to great lengths to
+forbid the use of ordered subselects. This breaks a very useful group of
+searches like "Give me things number 4 to 6 (ordered by name), and prefetch
+all their relations, no matter how many". While there is a hack which fools
+the syntax checker, the optimizer may B<still elect to break the subselect>.
+Testing has determined that while such breakage does occur (the test suite
+contains an explicit test which demonstrates the problem), it is relative
+rare. The benefits of ordered subselects are on the other hand too great to be
+outright disabled for MSSQL.
+
+Thus compromise between usability and perfection is the MSSQL-specific
+L<resultset attribute|DBIx::Class::ResultSet/ATTRIBUTES> C<unsafe_subselect_ok>.
+It is deliberately not possible to set this on the Storage level, as the user
+should inspect (and preferrably regression-test) the return of every such
+ResultSet individually. The example above would work if written like:
+
+ $rs->search ({}, {
+  unsafe_subselect_ok => 1,
+  prefetch => 'relation',
+  rows => 2,
+  offset => 3,
+ });
+
+If it is possible to rewrite the search() in a way that will avoid the need
+for this flag - you are urged to do so. If DBIC internals insist that an
+ordered subselect is necessary for an operation, and you believe there is a
+differnt/better way to get the same result - please file a bugreport.
+
 =head1 AUTHOR
 
 See L<DBIx::Class/CONTRIBUTORS>.