For more information on generating complex queries, see
L<SQL::Abstract/WHERE CLAUSES>.
+=head3 Arbitrary SQL through a custom ResultSource
+
+Sometimes you have to run arbitrary SQL because your query is too complex
+(e.g. it contains Unions, Sub-Selects, Stored Procedures, etc.) or has to
+be optimized for your database in a special way, but you still want to
+get the results as a L<DBIx::Class::ResultSet>.
+The recommended way to accomplish this is by defining a separate ResultSource
+for your query. You can then inject complete SQL statements using a scalar
+reference (this is a feature of L<SQL::Abstract>).
+
+Say you want to run a complex custom query on your user data, here's what
+you have to add to your User class:
+
+ package My::Schema::User;
+
+ use base qw/DBIx::Class/;
+
+ # ->load_components, ->table, ->add_columns, etc.
+
+ # Make a new ResultSource based on the User class
+ my $source = __PACKAGE__->result_source_instance();
+ my $new_source = $source->new( $source );
+ $new_source->source_name( 'UserFriendsComplex' );
+
+ # Hand in your query as a scalar reference
+ # It will be added as a sub-select after FROM,
+ # so pay attention to the surrounding brackets!
+ $new_source->name( \<<SQL );
+ ( SELECT u.* FROM user u
+ INNER JOIN user_friends f ON u.id = f.user_id
+ WHERE f.friend_user_id = ?
+ UNION
+ SELECT u.* FROM user u
+ INNER JOIN user_friends f ON u.id = f.friend_user_id
+ WHERE f.user_id = ? )
+ SQL
+
+ # Finally, register your new ResultSource with your Schema
+ My::Schema->register_source( 'UserFriendsComplex' => $new_source );
+
+Next, you can execute your complex query using bind parameters like this:
+
+ my $friends = [ $schema->resultset( 'UserFriendsComplex' )->search( {},
+ {
+ bind => [ 12345, 12345 ]
+ }
+ ) ];
+
+... and you'll get back a perfect L<DBIx::Class::ResultSet>.
+
=head3 Using specific columns
When you only want specific columns from a table, you can use
);
# Equivalent SQL:
- # SELECT name name, LENGTH( name ) name_length
+ # SELECT name name, LENGTH( name )
# FROM artist
-If your alias exists as a column in your base class (i.e. it was added
-with C<add_columns>), you just access it as normal. Our C<Artist>
-class has a C<name> column, so we just use the C<name> accessor:
+Note that the C< as > attribute has absolutely nothing to with the sql
+syntax C< SELECT foo AS bar > (see the documentation in
+L<DBIx::Class::ResultSet/ATTRIBUTES>). If your alias exists as a
+column in your base class (i.e. it was added with C<add_columns>), you
+just access it as normal. Our C<Artist> class has a C<name> column, so
+we just use the C<name> accessor:
my $artist = $rs->first();
my $name = $artist->name();
select => [
{ distinct => [ $source->columns ] }
],
- as => [ $source->columns ]
+ as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
}
);
# LEFT JOIN cd cds ON ( cds.artist = me.artistid )
# GROUP BY name
+Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
+are in any way unsure about the use of the attributes above (C< join
+>, C< select >, C< as > and C< group_by >).
+
=head3 Predefined searches
You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
deep using the same syntax as a multi-step join:
my $rs = $schema->resultset('Tag')->search(
- undef,
+ {},
{
prefetch => {
cd => 'artist'
my $tag = $rs->first;
print $tag->cd->artist->name;
+=head2 Columns of data
+
+If you want to find the sum of a particular column there are several
+ways, the obvious one is to use search:
+
+ my $rs = $schema->resultset('Items')->search(
+ {},
+ {
+ select => [ { sum => 'Cost' } ],
+ as => [ 'total_cost' ], # remember this 'as' is for DBIx::Class::ResultSet not SQL
+ }
+ );
+ my $tc = $rs->first->get_column('total_cost');
+
+Or, you can use the L<DBIx::Class::ResultSetColumn>, which gets
+returned when you ask the C<ResultSet> for a column using
+C<get_column>:
+
+ my $cost = $schema->resultset('Items')->get_column('Cost');
+ my $tc = $cost->sum;
+
+With this you can also do:
+
+ my $minvalue = $cost->min;
+ my $maxvalue = $cost->max;
+
+Or just iterate through the values of this column only:
+
+ while ( my $c = $cost->next ) {
+ print $c;
+ }
+
+ foreach my $c ($cost->all) {
+ print $c;
+ }
+
+C<ResultSetColumn> only has a limited number of built-in functions, if
+you need one that it doesn't have, then you can use the C<func> method
+instead:
+
+ my $avg = $cost->func('AVERAGE');
+
+This will cause the following SQL statement to be run:
+
+ SELECT AVERAGE(Cost) FROM Items me
+
+Which will of course only work if your database supports this function.
+See L<DBIx::Class::ResultSetColumn> for more documentation.
+
=head2 Using relationships
=head3 Create a new row in a related table
=head2 Transactions
As of version 0.04001, there is improved transaction support in
-L<DBIx::Class::Storage::DBI> and L<DBIx::Class::Schema>. Here is an
+L<DBIx::Class::Storage> and L<DBIx::Class::Schema>. Here is an
example of the recommended way to use it:
my $genus = $schema->resultset('Genus')->find(12);
=head2 Many-to-many relationships
-This is straightforward using L<DBIx::Class::Relationship::ManyToMany>:
+This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
package My::DB;
# ... set up connection ...
$attrs->{foo} = 'bar' unless defined $attrs->{foo};
- $class->next::method($attrs);
+ my $new = $class->next::method($attrs);
+
+ return $new;
}
For more information about C<next::method>, look in the L<Class::C3>
To make an object stringify itself as a single column, use something
like this (replace C<foo> with the column/method of your choice):
- use overload '""' => 'foo', fallback => 1;
+ use overload '""' => sub { shift->name}, fallback => 1;
For more complex stringification, you can use an anonymous subroutine:
=head2 Profiling
-When you enable L<DBIx::Class::Storage::DBI>'s debugging it prints the SQL
+When you enable L<DBIx::Class::Storage>'s debugging it prints the SQL
executed as well as notifications of query completion and transaction
begin/commit. If you'd like to profile the SQL you can subclass the
L<DBIx::Class::Storage::Statistics> class and write your own profiling
methods into the Admin class. There is a cleaner way to accomplish
this.
-Overriding the C<inflate_results()> method within the User proxy-class
+Overriding the C<inflate_result> method within the User proxy-class
gives us the effect we want. This method is called by
L<DBIx::Class::ResultSet> when inflating a result from storage. So we
grab the object being returned, inspect the values we are looking for,
### The statement below will print
print "I can do admin stuff\n" if $admin->can('do_admin_stuff');
+=head2 Skip object creation for faster results
+
+DBIx::Class is not built for speed, it's built for convenience and
+ease of use, but sometimes you just need to get the data, and skip the
+fancy objects.
+
+To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
+
+ my $rs = $schema->resultset('CD');
+
+ $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
+
+ my $hash_ref = $rs->find(1);
+
+Wasn't that easy?
+
+=head2 Get raw data for blindingly fast results
+
+If the C<inflate_result> solution above is not fast enough for you, you
+can use a DBIx::Class to return values exactly as they come out of the
+data base with none of the convenience methods wrapped round them.
+
+This is used like so:-
+
+ my $cursor = $rs->cursor
+ while (my @vals = $cursor->next) {
+ # use $val[0..n] here
+ }
+
+You will need to map the array offsets to particular columns (you can
+use the I<select> attribute of C<search()> to force ordering).
+
+=head2 Want to know if find_or_create found or created a row?
+
+Just use C<find_or_new> instead, then check C<in_storage>:
+
+ my $obj = $rs->find_or_new({ blah => 'blarg' });
+ unless ($obj->in_storage) {
+ $obj->insert;
+ # do whatever else you wanted if it was a new row
+ }
+
+=head3 Wrapping/overloading a column accessor
+
+Problem: Say you have a table "Camera" and want to associate a description
+with each camera. For most cameras, you'll be able to generate the description from
+the other columns. However, in a few special cases you may want to associate a
+custom description with a camera.
+
+Solution:
+
+In your database schema, define a description field in the "Camera" table that
+can contain text and null values.
+
+In DBIC, we'll overload the column accessor to provide a sane default if no
+custom description is defined. The accessor will either return or generate the
+description, depending on whether the field is null or not.
+
+First, in your "Camera" schema class, define the description field as follows:
+
+ __PACKAGE__->add_columns(description => { accessor => '_description' });
+
+Next, we'll define the accessor-wrapper subroutine:
+
+ sub description {
+ my $self = shift;
+
+ # If there is an update to the column, we'll let the original accessor
+ # deal with it.
+ return $self->_description(@_) if @_;
+
+ # Fetch the column value.
+ my $description = $self->_description;
+
+ # If there's something in the description field, then just return that.
+ return $description if defined $description && length $descripton;
+
+ # Otherwise, generate a description.
+ return $self->generate_description;
+ }
+
=cut