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;
- # _select_args does some shady action at a distance
- # see DBI.pm for more info
- my $sql_maker = $self->sql_maker;
- my ($op, $bind, $ident, $bind_attrs, $select, $cond, $order, $rows, $offset);
- {
- local $sql_maker->{_dbic_rs_attrs};
- ($op, $bind, $ident, $bind_attrs, $select, $cond, $order, $rows, $offset) = $self->_select_args(@_);
- }
+ my ($sql, $prep_bind, @rest) = $self->next::method (@_);
- if (
- ($rows || $offset)
- ||
- not scalar $sql_maker->_order_by_chunks ($order->{order_by})
- ) {
- # either limited RS or no ordering, just short circuit
- return $self->next::method (@_);
+ # see if this is an ordered subquery
+ my $attrs = $_[3];
+ 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 $max /xi;
}
- my ($sql, $prep_bind, @rest) = $self->next::method (@_);
- $sql =~ s/^ \s* SELECT \s/SELECT TOP 100 PERCENT /xi;
-
return wantarray
? ($sql, $prep_bind, @rest)
: \[ "($sql)", @$prep_bind ]
sub sqlt_type { 'SQLServer' }
-sub _sql_maker_opts {
- my ( $self, $opts ) = @_;
+sub _get_mssql_version {
+ my $self = shift;
+
+ my $data = $self->_get_dbh->selectrow_hashref('xp_msver ProductVersion');
- if ( $opts ) {
- $self->{_sql_maker_opts} = { %$opts };
+ if ($data->{Character_Value} =~ /^(\d+)\./) {
+ return $1;
+ } else {
+ $self->throw_exception(q{Your ProductVersion's Character_Value is missing or malformed!});
}
+}
- return { limit_dialect => 'MSRowNumberOver', %{$self->{_sql_maker_opts}||{}} };
+sub sql_maker {
+ my $self = shift;
+
+ unless ($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 $maker = $self->next::method (@_);
+ }
+
+ return $self->_sql_maker;
}
1;
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 preferably 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
+different/better way to get the same result - please file a bugreport.
+
=head1 AUTHOR
See L<DBIx::Class/CONTRIBUTORS>.
projects / dbsrgits/DBIx-Class.git / blobdiff