=head1 RECIPES
-=head2 Paged results
+=head2 Searching
-When you expect a large number of results, you can ask DBIx::Class for a paged
-resultset, which will fetch only a small number of records at a time:
+=head3 Paged results
- $rs = $schema->resultset('Artist')->search(
- {},
- {
- page => 1, # page to return (defaults to 1)
- rows => 10, # number of results per page
- },
- );
+When you expect a large number of results, you can ask L<DBIx::Class> for a
+paged resultset, which will fetch only a small number of records at a time:
- $rs->all(); # return all records for page 1
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ page => 1, # page to return (defaults to 1)
+ rows => 10, # number of results per page
+ },
+ );
-The "page" attribute does not have to be specified in your search:
+ return $rs->all(); # all records for page 1
- $rs = $schema->resultset('Artist')->search(
- {},
- {
- rows => 10,
- }
- );
+The C<page> attribute does not have to be specified in your search:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ rows => 10,
+ }
+ );
- $rs->page(1); # return DBIx::Class::ResultSet containing first 10 records
+ return $rs->page(1); # DBIx::Class::ResultSet containing first 10 records
In either of the above cases, you can return a L<Data::Page> object for the
-resultset (suitable for use in a TT template etc) using the pager() method:
+resultset (suitable for use in e.g. a template) using the C<pager> method:
- $pager = $rs->pager();
+ return $rs->pager();
-=head2 Complex searches
+=head3 Complex WHERE clauses
Sometimes you need to formulate a query using specific operators:
For more information on generating complex queries, see
L<SQL::Abstract/WHERE CLAUSES>.
-=head2 Disconnecting cleanly
-
-If you find yourself quitting an app with Control-C a lot during
-development, you might like to put the following signal handler in
-your main database class to make sure it disconnects cleanly:
-
- $SIG{INT} = sub {
- __PACKAGE__->storage->dbh->disconnect;
- };
-
-=head2 Using cols
+=head3 Using specific columns
-When you only want selected columns from a table, you can use "cols" to
-specify which ones you need (you could also use "select", but "cols" is the
-recommended way):
+When you only want selected columns from a table, you can use C<cols> to
+specify which ones you need:
- $rs = $schema->resultset('Artist')->search(
- {},
- {
- cols => [qw/ name /]
- }
- );
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ cols => [qw/ name /]
+ }
+ );
- # e.g.
- # SELECT artist.name FROM artist
+ # Equivalent SQL:
+ # SELECT artist.name FROM artist
-=head2 Using select and as
+=head3 Using database functions or stored procedures
-The combination of "select" and "as" is probably most useful when you want to
-return the result of a function or stored procedure as a column value. You use
-"select" to specify the source for your column value (e.g. a column name,
-function or stored procedure name). You then use "as" to set the column name
-you will use to access the returned value:
+The combination of C<select> and C<as> can be used to return the result of a
+database function or stored procedure as a column value. You use C<select> to
+specify the source for your column value (e.g. a column name, function, or
+stored procedure name). You then use C<as> to set the column name you will use
+to access the returned value:
- $rs = $schema->resultset('Artist')->search(
- {},
- {
- select => [ 'name', { LENGTH => 'name' } ],
- as => [qw/ name name_length /],
- }
- );
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ select => [ 'name', { LENGTH => 'name' } ],
+ as => [qw/ name name_length /],
+ }
+ );
- # e.g.
- # SELECT name name, LENGTH( name ) name_length
- # FROM artist
+ # Equivalent SQL:
+ # SELECT name name, LENGTH( name ) name_length
+ # FROM artist
If your alias exists as a column in your base class (i.e. it was added with
-add_columns()), you just access it as normal. Our Artist class has a "name"
-column, so we just use the "name" accessor:
+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();
+ my $artist = $rs->first();
+ my $name = $artist->name();
If on the other hand the alias does not correspond to an existing column, you
-can get the value using the get_column() accessor:
+can get the value using the C<get_column> accessor:
- my $name_length = $artist->get_column('name_length');
+ my $name_length = $artist->get_column('name_length');
-If you don't like using "get_column()", you can always create an accessor for
+If you don't like using C<get_column>, you can always create an accessor for
any of your aliases using either of these:
- # define accessor manually
- sub name_length { shift->get_column('name_length'); }
+ # Define accessor manually:
+ sub name_length { shift->get_column('name_length'); }
- # or use DBIx::Class::AccessorGroup
- __PACKAGE__->mk_group_accessors('column' => 'name_length');
-
-=head2 SELECT DISTINCT with multiple columns
-
- $rs = $schema->resultset('Foo')->search(
- {},
- {
- select => [
- { distinct => [ $source->columns ] }
- ],
- as => [ $source->columns ]
- }
- );
+ # Or use DBIx::Class::AccessorGroup:
+ __PACKAGE__->mk_group_accessors('column' => 'name_length');
-=head2 SELECT COUNT(DISTINCT colname)
+=head3 SELECT DISTINCT with multiple columns
- $rs = $schema->resultset('Foo')->search(
- {},
- {
- select => [
- { count => { distinct => 'colname' } }
- ],
- as => [ 'count' ]
- }
- );
+ my $rs = $schema->resultset('Foo')->search(
+ {},
+ {
+ select => [
+ { distinct => [ $source->columns ] }
+ ],
+ as => [ $source->columns ]
+ }
+ );
-=head2 Grouping results
+=head3 SELECT COUNT(DISTINCT colname)
-DBIx::Class supports GROUP BY as follows:
+ my $rs = $schema->resultset('Foo')->search(
+ {},
+ {
+ select => [
+ { count => { distinct => 'colname' } }
+ ],
+ as => [ 'count' ]
+ }
+ );
- $rs = $schema->resultset('Artist')->search(
- {},
- {
- join => [qw/ cds /],
- select => [ 'name', { count => 'cds.cdid' } ],
- as => [qw/ name cd_count /],
- group_by => [qw/ name /]
- }
- );
+=head3 Grouping results
+
+L<DBIx::Class> supports C<GROUP BY> as follows:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ join => [qw/ cds /],
+ select => [ 'name', { count => 'cds.cdid' } ],
+ as => [qw/ name cd_count /],
+ group_by => [qw/ name /]
+ }
+ );
- # e.g.
- # SELECT name, COUNT( cds.cdid ) FROM artist me
- # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
- # GROUP BY name
+ # Equivalent SQL:
+ # SELECT name, COUNT( cds.cdid ) FROM artist me
+ # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
+ # GROUP BY name
=head2 Using joins and prefetch
-You can use the "join" attribute to allow searching on, or sorting your
-results by, one or more columns in a related table. To return
-all CDs matching a particular artist name:
+You can use the C<join> attribute to allow searching on, or sorting your
+results by, one or more columns in a related table. To return all CDs matching
+a particular artist name:
- my $rs = $schema->resultset('CD')->search(
- {
- 'artist.name' => 'Bob Marley'
- },
- {
- join => [qw/artist/], # join the artist table
- }
- );
-
- # equivalent SQL:
- # SELECT cd.* FROM cd
- # JOIN artist ON cd.artist = artist.id
- # WHERE artist.name = 'Bob Marley'
-
-If required, you can now sort on any column in the related table(s) by
-including it in your "order_by" attribute:
-
- my $rs = $schema->resultset('CD')->search(
- {
- 'artist.name' => 'Bob Marley'
- },
- {
- join => [qw/ artist /],
- order_by => [qw/ artist.name /]
- }
- };
+ my $rs = $schema->resultset('CD')->search(
+ {
+ 'artist.name' => 'Bob Marley'
+ },
+ {
+ join => [qw/artist/], # join the artist table
+ }
+ );
+
+ # Equivalent SQL:
+ # SELECT cd.* FROM cd
+ # JOIN artist ON cd.artist = artist.id
+ # WHERE artist.name = 'Bob Marley'
+
+If required, you can now sort on any column in the related tables by including
+it in your C<order_by> attribute:
+
+ my $rs = $schema->resultset('CD')->search(
+ {
+ 'artist.name' => 'Bob Marley'
+ },
+ {
+ join => [qw/ artist /],
+ order_by => [qw/ artist.name /]
+ }
+ };
- # equivalent SQL:
- # SELECT cd.* FROM cd
- # JOIN artist ON cd.artist = artist.id
- # WHERE artist.name = 'Bob Marley'
- # ORDER BY artist.name
+ # Equivalent SQL:
+ # SELECT cd.* FROM cd
+ # JOIN artist ON cd.artist = artist.id
+ # WHERE artist.name = 'Bob Marley'
+ # ORDER BY artist.name
-Note that the "join" attribute should only be used when you need to search or
-sort using columns in a related table. Joining related tables when you
-only need columns from the main table will make performance worse!
+Note that the C<join> attribute should only be used when you need to search or
+sort using columns in a related table. Joining related tables when you only
+need columns from the main table will make performance worse!
-Now let's say you want to display a list of CDs, each with the name of
-the artist. The following will work fine:
+Now let's say you want to display a list of CDs, each with the name of the
+artist. The following will work fine:
- while (my $cd = $rs->next) {
- print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
- }
+ while (my $cd = $rs->next) {
+ print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
+ }
-There is a problem however. We have searched both cd and artist tables in our
-main query, but we have only returned data from the cd table. To get the artist
-name for any of the CD objects returned, DBIx::Class will go back to the
-database:
+There is a problem however. We have searched both the C<cd> and C<artist> tables
+in our main query, but we have only returned data from the C<cd> table. To get
+the artist name for any of the CD objects returned, L<DBIx::Class> will go back
+to the database:
- SELECT artist.* FROM artist WHERE artist.id = ?
+ SELECT artist.* FROM artist WHERE artist.id = ?
A statement like the one above will run for each and every CD returned by our
main query. Five CDs, five extra queries. A hundred CDs, one hundred extra
queries!
-Thankfully, DBIx::Class has a "prefetch" attribute to solve this problem. This
-allows you to fetch results from a related table as well as the main table
+Thankfully, L<DBIx::Class> has a C<prefetch> attribute to solve this problem.
+This allows you to fetch results from a related table as well as the main table
for your class:
- my $rs = $schema->resultset('CD')->search(
- {
- 'artist.name' => 'Bob Marley'
- },
- {
- join => [qw/ artist /],
- order_by => [qw/ artist.name /],
- prefetch => [qw/ artist /] # return artist data too!
- }
- );
+ my $rs = $schema->resultset('CD')->search(
+ {
+ 'artist.name' => 'Bob Marley'
+ },
+ {
+ join => [qw/ artist /],
+ order_by => [qw/ artist.name /],
+ prefetch => [qw/ artist /] # return artist data too!
+ }
+ );
- # equivalent SQL (note SELECT from both "cd" and "artist")
- # SELECT cd.*, artist.* FROM cd
- # JOIN artist ON cd.artist = artist.id
- # WHERE artist.name = 'Bob Marley'
- # ORDER BY artist.name
+ # Equivalent SQL (note SELECT from both "cd" and "artist"):
+ # SELECT cd.*, artist.* FROM cd
+ # JOIN artist ON cd.artist = artist.id
+ # WHERE artist.name = 'Bob Marley'
+ # ORDER BY artist.name
The code to print the CD list remains the same:
- while (my $cd = $rs->next) {
- print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
- }
+ while (my $cd = $rs->next) {
+ print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
+ }
-DBIx::Class has now prefetched all matching data from the "artist" table,
+L<DBIx::Class> has now prefetched all matching data from the C<artist> table,
so no additional SQL statements are executed. You now have a much more
efficient query.
-Note that as of DBIx::Class 0.04, "prefetch" cannot be used with has_many
-relationships. You will get an error along the lines of "No accessor for
-prefetched ..." if you try.
+Note that as of L<DBIx::Class> 0.04, C<prefetch> cannot be used with
+C<has_many> relationships. You will get an error along the lines of "No
+accessor for prefetched ..." if you try.
-Note that "prefetch" should only be used when you know you will
+Also note that C<prefetch> should only be used when you know you will
definitely use data from a related table. Pre-fetching related tables when you
only need columns from the main table will make performance worse!
-=head2 Multi-step joins
+=head3 Multi-step joins
Sometimes you want to join more than one relationship deep. In this example,
-we want to find all Artist objects who have CDs whose LinerNotes contain a
-specific string:
-
- # Artist->has_many('cds' => 'CD', 'artist');
- # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
-
- $rs = $schema->resultset('Artist')->search(
- {
- 'liner_notes.notes' => { 'like', '%some text%' },
- },
- {
- join => {
- 'cds' => 'liner_notes'
- }
- }
- );
+we want to find all C<Artist> objects who have C<CD>s whose C<LinerNotes>
+contain a specific string:
+
+ # Relationships defined elsewhere:
+ # Artist->has_many('cds' => 'CD', 'artist');
+ # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
+
+ my $rs = $schema->resultset('Artist')->search(
+ {
+ 'liner_notes.notes' => { 'like', '%some text%' },
+ },
+ {
+ join => {
+ 'cds' => 'liner_notes'
+ }
+ }
+ );
- # equivalent SQL
- # SELECT artist.* FROM artist
- # JOIN ( cd ON artist.id = cd.artist )
- # JOIN ( liner_notes ON cd.id = liner_notes.cd )
- # WHERE liner_notes.notes LIKE '%some text%'
+ # Equivalent SQL:
+ # SELECT artist.* FROM artist
+ # JOIN ( cd ON artist.id = cd.artist )
+ # JOIN ( liner_notes ON cd.id = liner_notes.cd )
+ # WHERE liner_notes.notes LIKE '%some text%'
Joins can be nested to an arbitrary level. So if we decide later that we
want to reduce the number of Artists returned based on who wrote the liner
notes:
- # LinerNotes->belongs_to('author' => 'Person');
-
- $rs = $schema->resultset('Artist')->search(
- {
- 'liner_notes.notes' => { 'like', '%some text%' },
- 'author.name' => 'A. Writer'
- },
- {
- join => {
- 'cds' => {
- 'liner_notes' => 'author'
- }
- }
+ # Relationship defined elsewhere:
+ # LinerNotes->belongs_to('author' => 'Person');
+
+ my $rs = $schema->resultset('Artist')->search(
+ {
+ 'liner_notes.notes' => { 'like', '%some text%' },
+ 'author.name' => 'A. Writer'
+ },
+ {
+ join => {
+ 'cds' => {
+ 'liner_notes' => 'author'
}
- );
+ }
+ }
+ );
- # equivalent SQL
- # SELECT artist.* FROM artist
- # JOIN ( cd ON artist.id = cd.artist )
- # JOIN ( liner_notes ON cd.id = liner_notes.cd )
- # JOIN ( author ON author.id = liner_notes.author )
- # WHERE liner_notes.notes LIKE '%some text%'
- # AND author.name = 'A. Writer'
+ # Equivalent SQL:
+ # SELECT artist.* FROM artist
+ # JOIN ( cd ON artist.id = cd.artist )
+ # JOIN ( liner_notes ON cd.id = liner_notes.cd )
+ # JOIN ( author ON author.id = liner_notes.author )
+ # WHERE liner_notes.notes LIKE '%some text%'
+ # AND author.name = 'A. Writer'
=head2 Transactions
This is straightforward using L<DBIx::Class::Relationship::ManyToMany>:
- package My::DB;
- # set up connection here...
-
- package My::User;
- use base 'My::DB';
- __PACKAGE__->table('user');
- __PACKAGE__->add_columns(qw/id name/);
- __PACKAGE__->set_primary_key('id');
- __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
- __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
-
- package My::UserAddress;
- use base 'My::DB';
- __PACKAGE__->table('user_address');
- __PACKAGE__->add_columns(qw/user address/);
- __PACKAGE__->set_primary_key(qw/user address/);
- __PACKAGE__->belongs_to('user' => 'My::User');
- __PACKAGE__->belongs_to('address' => 'My::Address');
-
- package My::Address;
- use base 'My::DB';
- __PACKAGE__->table('address');
- __PACKAGE__->add_columns(qw/id street town area_code country/);
- __PACKAGE__->set_primary_key('id');
- __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
- __PACKAGE__->many_to_many('users' => 'user_address', 'user');
-
- $rs = $user->addresses(); # get all addresses for a user
- $rs = $address->users(); # get all users for an address
-
-=head2 Setting default values
+ package My::DB;
+ # ... set up connection ...
+
+ package My::User;
+ use base 'My::DB';
+ __PACKAGE__->table('user');
+ __PACKAGE__->add_columns(qw/id name/);
+ __PACKAGE__->set_primary_key('id');
+ __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'user');
+ __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
+
+ package My::UserAddress;
+ use base 'My::DB';
+ __PACKAGE__->table('user_address');
+ __PACKAGE__->add_columns(qw/user address/);
+ __PACKAGE__->set_primary_key(qw/user address/);
+ __PACKAGE__->belongs_to('user' => 'My::User');
+ __PACKAGE__->belongs_to('address' => 'My::Address');
+
+ package My::Address;
+ use base 'My::DB';
+ __PACKAGE__->table('address');
+ __PACKAGE__->add_columns(qw/id street town area_code country/);
+ __PACKAGE__->set_primary_key('id');
+ __PACKAGE__->has_many('user_address' => 'My::UserAddress', 'address');
+ __PACKAGE__->many_to_many('users' => 'user_address', 'user');
+
+ $rs = $user->addresses(); # get all addresses for a user
+ $rs = $address->users(); # get all users for an address
+
+=head2 Setting default values for a row
It's as simple as overriding the C<new> method. Note the use of
C<next::method>.
use overload '""' => 'foo', fallback => 1;
+=head2 Disconnecting cleanly
+
+If you find yourself quitting an app with Control-C a lot during
+development, you might like to put the following signal handler in
+your main database class to make sure it disconnects cleanly:
+
+ $SIG{INT} = sub {
+ __PACKAGE__->storage->dbh->disconnect;
+ };
+
=cut
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