X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FStorage%2FDBI%2FMSSQL.pm;h=5f17153fe5f566c6396998c388c31c7044bb5fe1;hb=ff153e241d4990c6332359d942385d11019f0018;hp=ea1269a8cdb1c052a0c6b62749a1913080e21f1a;hpb=6de07ea386016c9a45b51ad919ac22563bb4d9d6;p=dbsrgits%2FDBIx-Class.git diff --git a/lib/DBIx/Class/Storage/DBI/MSSQL.pm b/lib/DBIx/Class/Storage/DBI/MSSQL.pm index ea1269a..5f17153 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(); @@ -190,10 +190,10 @@ 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}) ) { + if ( scalar $self->_parse_order_by ($attrs->{order_by}) ) { $self->throw_exception( - 'An ordered subquery encountered. Please see "Ordered Subqueries" in DBIx::Class::Storage::DBI::MSSQL - ') unless $attrs->{unsafe_subquery}; + '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; } @@ -232,24 +232,14 @@ sub build_datetime_parser { sub sqlt_type { 'SQLServer' } -sub _get_mssql_version { - my $self = shift; - - my $data = $self->_get_dbh->selectrow_hashref('xp_msver ProductVersion'); - - if ($data->{Character_Value} =~ /^(\d+)\./) { - return $1; - } else { - $self->throw_exception(q{Your ProductVersion's Character_Value is missing or malformed!}); - } -} - sub sql_maker { my $self = shift; unless ($self->_sql_maker) { unless ($self->{_sql_maker_opts}{limit_dialect}) { - my $version = eval { $self->_get_mssql_version; } || 0; + + my ($version) = $self->_server_info->{dbms_ver} =~ /^(\d+)/; + $version ||= 0; $self->{_sql_maker_opts} = { limit_dialect => ($version >= 9 ? 'RowNumberOver' : 'Top'), @@ -263,6 +253,21 @@ sub sql_maker { return $self->_sql_maker; } +sub _ping { + my $self = shift; + + my $dbh = $self->_dbh or return 0; + + local $dbh->{RaiseError} = 1; + local $dbh->{PrintError} = 0; + + eval { + $dbh->do('select 1'); + }; + + return $@ ? 0 : 1; +} + 1; =head1 NAME @@ -308,44 +313,53 @@ $table_name ON>. Unfortunately this operation in MSSQL requires the C privilege, which is normally not included in the standard write-permissions. -=head2 Ordered Subqueries +=head2 Ordered Subselects + +If you attempted the following query (among many others) in Microsoft SQL +Server - # this is deemed unsafe and throws under MSSQL $rs->search ({}, { prefetch => 'relation', rows => 2, offset => 3, }); - # however this should work (but please check what comes back from the db) +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 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. +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 C. +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_subquery => 1, + unsafe_subselect_ok => 1, prefetch => 'relation', rows => 2, offset => 3, }); -DBIC can do truly wonderful things with the aid of subqueries, and does so -automatically when necessary. Especially useful are ordered subqueries, -which allow things like "Give me things number 4 to 6 (ordered by name), and -prefetch all their relationss, no matter how many". In its pursuit of standards -Microsft SQL Server goes to great lengths to forbid the use of ordered -subqueries. While there is a hack which fools the syntax checker, the optimizer -may B. 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 -subqueries are on the other hand too great to be outright disabled for MSSQL. - -Thus compromise between usability and perfection is the MSSQL-specific -L C. -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. - 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 subquery is necessary for an operation, and you believe there is a -differnt way to express the query - please file a bugreport. +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