=head1 NAME
-DBIx::Class::Manual::Cookbook - Misc recipes
+DBIx::Class::Manual::Cookbook - Miscellaneous recipes
-=head1 DESCRIPTION
+=head1 RECIPES
-Things that could be handy
+=head2 Searching
-=head1 RECIPES
+=head3 Paged results
+
+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:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ page => 1, # page to return (defaults to 1)
+ rows => 10, # number of results per page
+ },
+ );
+
+ return $rs->all(); # all records for page 1
+
+The C<page> attribute does not have to be specified in your search:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ rows => 10,
+ }
+ );
+
+ 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 e.g. a template) using the C<pager> method:
+
+ return $rs->pager();
+
+=head3 Complex WHERE clauses
+
+Sometimes you need to formulate a query using specific operators:
+
+ my @albums = $schema->resultset('Album')->search({
+ artist => { 'like', '%Lamb%' },
+ title => { 'like', '%Fear of Fours%' },
+ });
+
+This results in something like the following C<WHERE> clause:
+
+ WHERE artist LIKE '%Lamb%' AND title LIKE '%Fear of Fours%'
+
+Other queries might require slightly more complex logic:
+
+ my @albums = $schema->resultset('Album')->search({
+ -or => [
+ -and => [
+ artist => { 'like', '%Smashing Pumpkins%' },
+ title => 'Siamese Dream',
+ ],
+ artist => 'Starchildren',
+ ],
+ });
+
+This results in the following C<WHERE> clause:
+
+ WHERE ( artist LIKE '%Smashing Pumpkins%' AND title = 'Siamese Dream' )
+ OR artist = 'Starchildren'
+
+For more information on generating complex queries, see
+L<SQL::Abstract/WHERE CLAUSES>.
+
+=head3 Using specific columns
+
+When you only want selected columns from a table, you can use C<cols> to
+specify which ones you need:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ cols => [qw/ name /]
+ }
+ );
+
+ # Equivalent SQL:
+ # SELECT artist.name FROM artist
+
+=head3 Using database functions or stored procedures
+
+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:
+
+ my $rs = $schema->resultset('Artist')->search(
+ {},
+ {
+ select => [ 'name', { LENGTH => 'name' } ],
+ as => [qw/ name name_length /],
+ }
+ );
+
+ # 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
+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();
+
+If on the other hand the alias does not correspond to an existing column, you
+can get the value using the C<get_column> accessor:
+
+ my $name_length = $artist->get_column('name_length');
+
+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'); }
+
+ # Or use DBIx::Class::AccessorGroup:
+ __PACKAGE__->mk_group_accessors('column' => 'name_length');
+
+=head3 SELECT DISTINCT with multiple columns
+
+ my $rs = $schema->resultset('Foo')->search(
+ {},
+ {
+ select => [
+ { distinct => [ $source->columns ] }
+ ],
+ as => [ $source->columns ]
+ }
+ );
+
+=head3 SELECT COUNT(DISTINCT colname)
+
+ my $rs = $schema->resultset('Foo')->search(
+ {},
+ {
+ select => [
+ { count => { distinct => 'colname' } }
+ ],
+ as => [ 'count' ]
+ }
+ );
+
+=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 /]
+ }
+ );
+
+ # 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 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 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
+
+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:
+
+ while (my $cd = $rs->next) {
+ print "CD: " . $cd->title . ", Artist: " . $cd->artist->name;
+ }
+
+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 = ?
+
+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, 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!
+ }
+ );
+
+ # 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;
+ }
+
+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 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.
+
+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!
+
+=head3 Multi-step joins
+
+Sometimes you want to join more than one relationship deep. In this example,
+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%'
+
+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:
+
+ # 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'
+
+=head2 Transactions
+
+As of version 0.04001, there is improved transaction support in
+L<DBIx::Class::Storage::DBI>. Here is an example of the recommended
+way to use it:
+
+ my $genus = Genus->find(12);
+ eval {
+ MyDB->txn_begin;
+ $genus->add_to_species({ name => 'troglodyte' });
+ $genus->wings(2);
+ $genus->update;
+ cromulate($genus); # Can have a nested transation
+ MyDB->txn_commit;
+ };
+ if ($@) {
+ # Rollback might fail, too
+ eval {
+ MyDB->txn_rollback
+ };
+ }
+
+Currently, a nested commit will do nothing and a nested rollback will
+die. The code at each level must be sure to call rollback in the case
+of an error, to ensure that the rollback will propagate to the top
+level and be issued. Support for savepoints and for true nested
+transactions (for databases that support them) will hopefully be added
+in the future.
+
+=head2 Many-to-many relationships
+
+This is straightforward using L<DBIx::Class::Relationship::ManyToMany>:
+
+ 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>.
+
+ sub new {
+ my ( $class, $attrs ) = @_;
+
+ $attrs->{foo} = 'bar' unless defined $attrs->{foo};
+
+ $class->next::method($attrs);
+ }
+
+=head2 Stringification
+
+Employ the standard stringification technique by using the C<overload>
+module. Replace C<foo> with the column/method of your choice.
+
+ 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;
+ };
+
+=head2 Schema import/export
+
+This functionality requires you to have L<SQL::Translator> (also known as
+"SQL Fairy") installed.
+
+To create a DBIx::Class schema from an existing database:
+
+ sqlt --from DBI
+ --to DBIx::Class::File
+ --prefix "MySchema" > MySchema.pm
+
+To create a MySQL database from an existing L<DBIx::Class> schema, convert the
+schema to MySQL's dialect of SQL:
+
+ sqlt --from DBIx::Class --to MySQL --DBIx::Class "MySchema.pm" > Schema1.sql
+
+And import using the mysql client:
+
+ mysql -h "host" -D "database" -u "user" -p < Schema1.sql
+
+=head2 Easy migration from class-based to schema-based setup
+
+You want to start using the schema-based approach to L<DBIx::Class>
+(see L<SchemaIntro.pod>), but have an established class-based setup with lots
+of existing classes that you don't want to move by hand. Try this nifty script
+instead:
+
+ use MyDB;
+ use SQL::Translator;
+
+ my $schema = MyDB->schema_instance;
+
+ my $translator = SQL::Translator->new(
+ debug => $debug || 0,
+ trace => $trace || 0,
+ no_comments => $no_comments || 0,
+ show_warnings => $show_warnings || 0,
+ add_drop_table => $add_drop_table || 0,
+ validate => $validate || 0,
+ parser_args => {
+ 'DBIx::Schema' => $schema,
+ }
+ producer_args => {
+ 'prefix' => 'My::Schema',
+ }
+ );
+
+ $translator->parser('DBIx::Class');
+ $translator->producer('DBIx::Class::File');
+
+ my $output = $translator->translate(@args) or die
+ "Error: " . $translator->error;
+
+ print $output;
+
+You could use L<Module::Find> to search for all subclasses in the MyDB::*
+namespace, which is currently left as an excercise for the reader.
+
+=head2 Schema versioning
-=item Input validation.
+The following example shows simplistically how you might use DBIx::Class to
+deploy versioned schemas to your customers. The basic process is as follows:
-=item Using joins
+1) Create a DBIx::Class schema
+2) Save the schema
+3) Deploy to customers
+4) Modify schema to change functionality
+5) Deploy update to customers
-=item Many-to-many relationships
+=head3 Create a DBIx::Class schema
-This is not as easy as it could be, but it's possible. Here's an example to
-illustrate:
+This can either be done manually, or generated from an existing database as
+described under C<Schema import/export>.
- # Set up inherited connection information
- package MyApp::DBIC;
- use base qw/DBIx::Class/;
+=head3 Save the schema
- __PACKAGE__->load_components(qw/PK::Auto::SQLite Core DB/);
- __PACKAGE__->connection(...);
+Use C<sqlt> to transform your schema into an SQL script suitable for your
+customer's database. E.g. for MySQL:
- # Set up a class for the 'authors' table
- package MyApp::DBIC::Author;
- use base qw/MyApp::DBIC/;
+ sqlt --from DBIx::Class
+ --to MySQL
+ --DBIx::Class "MySchema.pm" > Schema1.mysql.sql
- __PACKAGE__->table('authors');
- __PACKAGE__->add_columns(qw/authID first_name last_name/);
- __PACKAGE__->set_primary_key(qw/authID/);
+If you need to target databases from multiple vendors, just generate an SQL
+script suitable for each. To support PostgreSQL too:
- # Define relationship to the link table
- __PACKAGE__->has_many('b2a' => 'MyApp::DBIC::Book2Author', 'authID');
+ sqlt --from DBIx::Class
+ --to PostgreSQL
+ --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql
- # Create the accessor for books from the ::Author class
- sub books {
- my ($self) = @_;
- return MyApp::DBIC::Book->search(
- { 'b2a.authID' => $self->authID }, # WHERE clause
- { join => 'b2a' } # join condition (part of search attrs)
- # 'b2a' refers to the relationship named earlier in the Author class.
- # 'b2a.authID' refers to the authID column of the b2a relationship,
- # which becomes accessible in the search by being joined.
- );
- }
+=head3 Deploy to customers
- # define the link table class
- package MyApp::DBIC::Book2Author;
- use base qw/MyApp::DBIC/;
+There are several ways you could deploy your schema. These are probably
+beyond the scope of this recipe, but might include:
- __PACKAGE__->table('book2author');
- __PACKAGE__->add_columns(qw/bookID authID/);
- __PACKAGE__->set_primary_key(qw/bookID authID/);
+1) Require customer to apply manually using their RDBMS.
+2) Package along with your app, making database dump/schema update/tests
+all part of your install.
- __PACKAGE__->belongs_to('authID' => 'MyApp::DBIC::Author');
- __PACKAGE__->belongs_to('bookID' => 'MyApp::DBIC::Book');
+=head3 Modify the schema to change functionality
- package MyApp::DBIC::Book;
- use base qw/MyApp::DBIC/;
+As your application evolves, it may be necessary to modify your schema to
+change functionality. Once the changes are made to your schema in DBIx::Class,
+export the modified schema as before, taking care not to overwrite the original:
- __PACKAGE__->table('books');
- __PACKAGE__->add_columns(qw/bookID title edition isbn publisher year/);
- __PACKAGE__->set_primary_key(qw/bookID/);
-
- __PACKAGE__->has_many('b2a' => 'MyApp::DBIC::Book2Author', 'bookID');
+ sqlt --from DBIx::Class
+ --to MySQL
+ --DBIx::Class "Anything.pm" > Schema2.mysql.sql
- sub authors {
- my ($self) = @_;
- return MyApp::DBIC::Author->search(
- { 'b2a.bookID' => $self->bookID }, # WHERE clause
- { join => 'b2a' }); # join condition (part of search attrs)
- }
+Next, use sqlt-diff to create an SQL script that will update the customer's
+database schema:
- # So the above search returns an author record where the bookID field of the
- # book2author table equals the bookID of the books (using the bookID
- # relationship table
+ sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql
-=item Advanced Exception handling
+=head3 Deploy update to customers
-=item Transactions
+The schema update can be deployed to customers using the same method as before.
-=back
+=cut
projects / dbsrgits/DBIx-Class.git / blobdiff