X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FManual%2FCookbook.pod;h=52bb889691b9a7b8675dc75ff1d59855182f3d28;hb=8b50216ef0fb096f61405a93a96b68a1d1b62bf4;hp=48edc40df513774fbf4270383b02078fca9871fe;hpb=8091aa9182ff763aa607dd82f4d61b99f8adab37;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Manual/Cookbook.pod b/lib/DBIx/Class/Manual/Cookbook.pod
index 48edc40..52bb889 100644
--- a/lib/DBIx/Class/Manual/Cookbook.pod
+++ b/lib/DBIx/Class/Manual/Cookbook.pod
@@ -1,113 +1,1197 @@
 =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
 
-=head2 Disconnecting cleanly
+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(
+    undef,
+    {
+      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(
+    undef,
+    {
+      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 specific columns from a table, you can use
+C<columns> to specify which ones you need. This is useful to avoid
+loading columns with large amounts of data that you aren't about to
+use anyway:
+
+  my $rs = $schema->resultset('Artist')->search(
+    undef,
+    {
+      columns => [qw/ name /]
+    }
+  );
+
+  # Equivalent SQL:
+  # SELECT artist.name FROM artist
+
+This is a shortcut for C<select> and C<as>, see below. C<columns>
+cannot be used together with C<select> and C<as>.
+
+=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 )
+  # FROM artist
+
+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();
+
+If on the other hand the alias does not correspond to an existing column, you
+have to fetch 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 ] # remember 'as' is not the same as SQL AS :-)
+    }
+  );
+
+  my $count = $rs->next->get_column('count');
 
-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:
+=head3 SELECT COUNT(DISTINCT colname)
 
-    $SIG{INT} = sub {
-        __PACKAGE__->storage->dbh->disconnect;
-    };
+  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 = $schema->resultset('Artist')->search(
+    {},
+    {
+      join     => [qw/ cds /],
+      select   => [ 'name', { count => 'cds.cdid' } ],
+      as       => [qw/ name cd_count /],
+      group_by => [qw/ name /]
+    }
+  );
+
+  # Equivalent SQL:
+  # SELECT name, COUNT( cds.cdid ) FROM artist me
+  # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
+  # GROUP BY name
+
+Please see L<DBIx::Class::ResultSet/ATTRIBUTES> documentation if you
+are in any way unsure about the use of the attributes above (C< join
+>, C< select >, C< as > and C< group_by >).
+
+=head3 Predefined searches
+
+You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
+and define often used searches as methods:
+
+  package My::DBIC::ResultSet::CD;
+  use strict;
+  use warnings;
+  use base 'DBIx::Class::ResultSet';
+
+  sub search_cds_ordered {
+      my ($self) = @_;
+
+      return $self->search(
+          {},
+          { order_by => 'name DESC' },
+      );
+  }
+
+  1;
+
+To use your resultset, first tell DBIx::Class to create an instance of it
+for you, in your My::DBIC::Schema::CD class:
+
+  __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
+
+Then call your new method in your code:
+
+   my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
+
+
+=head3 Predefined searches without writing a ResultSet class
+
+Alternatively you can automatically generate a DBIx::Class::ResultSet
+class by using the ResultSetManager component and tagging your method
+as ResultSet:
+
+  __PACKAGE__->load_components(qw/ ResultSetManager Core /);
+
+  sub search_cds_ordered : ResultSet {
+      my ($self) = @_;
+      return $self->search(
+          {},
+          { order_by => 'name DESC' },
+      );
+  } 
+
+Then call your method in the same way from your code:
+
+   my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
 
 =head2 Using joins and prefetch
 
-See L<DBIx::Class::ResultSet/Attributes>.
+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 related tables in advance:
+
+  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> 0.05999_01, C<prefetch> I<can> be used with
+C<has_many> relationships.
+
+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 Multi-step prefetch
+
+From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
+deep using the same syntax as a multi-step join:
+
+  my $rs = $schema->resultset('Tag')->search(
+    {},
+    {
+      prefetch => {
+        cd => 'artist'
+      }
+    }
+  );
+
+  # Equivalent SQL:
+  # SELECT tag.*, cd.*, artist.* FROM tag
+  # JOIN cd ON tag.cd = cd.cdid
+  # JOIN artist ON cd.artist = artist.artistid
+
+Now accessing our C<cd> and C<artist> relationships does not need additional
+SQL statements:
+
+  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
+
+  my $book->create_related('author', { name => 'Fred'});
+
+=head3 Search in a related table
+
+Only searches for books named 'Titanic' by the author in $author.
+
+  my $author->search_related('books', { name => 'Titanic' });
+
+=head3 Delete data in a related table
+
+Deletes only the book named Titanic by the author in $author.
+
+  my $author->delete_related('books', { name => 'Titanic' });
+
+=head3 Ordering a relationship result set
+
+If you always want a relation to be ordered, you can specify this when you 
+create the relationship.
+
+To order C<< $book->pages >> by descending page_number.
+
+  Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
+
+
 
 =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 $obj = Genus->find(12);
-    eval {
-        MyDB->txn_begin;
-        $obj->add_to_species({ name => 'troglodyte' });
-        $obj->wings(2);
-        $obj->update;
-        cromulate($obj); # can have a nested transation
-        MyDB->txn_commit;
-    };
-    if ($@) { eval { MyDB->txn_rollback } } # rollback might fail, too
-
-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.
+L<DBIx::Class::Storage::DBI> and L<DBIx::Class::Schema>.  Here is an
+example of the recommended way to use it:
+
+  my $genus = $schema->resultset('Genus')->find(12);
+
+  my $coderef2 = sub {
+    $genus->extinct(1);
+    $genus->update;
+  };
+
+  my $coderef1 = sub {
+    $genus->add_to_species({ name => 'troglodyte' });
+    $genus->wings(2);
+    $genus->update;
+    $schema->txn_do($coderef2); # Can have a nested transaction
+    return $genus->species;
+  };
+
+  my $rs;
+  eval {
+    $rs = $schema->txn_do($coderef1);
+  };
+
+  if ($@) {                             # Transaction failed
+    die "the sky is falling!"           #
+      if ($@ =~ /Rollback failed/);     # Rollback failed
+
+    deal_with_failed_transaction();
+  }
+
+Nested transactions will work as expected. That is, only the outermost
+transaction will actually issue a commit to the $dbh, and a rollback
+at any level of any transaction will cause the entire nested
+transaction to fail. 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 not as easy as it could be, but it's possible. Here's an example to 
-illustrate:
-
-	# Set up inherited connection information
-	package MyApp::DBIC; 
-	use base qw/DBIx::Class/;
-
-	__PACKAGE__->load_components(qw/PK::Auto::SQLite Core DB/);
-	__PACKAGE__->connection(...);
-
-	# Set up a class for the 'authors' table
-	package MyApp::DBIC::Author;
-	use base qw/MyApp::DBIC/;
-
-	__PACKAGE__->table('authors');
-	__PACKAGE__->add_columns(qw/authID first_name last_name/);
-	__PACKAGE__->set_primary_key(qw/authID/);
-
-	# Define relationship to the link table
-	__PACKAGE__->has_many('b2a' => 'MyApp::DBIC::Book2Author', 'authID');
-
-	# Create the accessor for books from the ::Author class
-	sub books {
-	  my ($self) = @_;
-	  return MyApp::DBIC::Book->search(
-		{ 'b2a.authID' => $self->authID }, # WHERE clause
-		{ join => 'b2a' } # join condition (part of search attrs)
-	    # 'b2a' refers to the relationship named earlier in the Author class.
-		# 'b2a.authID' refers to the authID column of the b2a relationship,
-		# which becomes accessible in the search by being joined.  
-	  );
-	}
-
-	# define the link table class
-	package MyApp::DBIC::Book2Author;
-	use base qw/MyApp::DBIC/;
-
-	__PACKAGE__->table('book2author');
-	__PACKAGE__->add_columns(qw/bookID authID/);
-	__PACKAGE__->set_primary_key(qw/bookID authID/);
-
-	__PACKAGE__->belongs_to('authID' => 'MyApp::DBIC::Author');
-	__PACKAGE__->belongs_to('bookID' => 'MyApp::DBIC::Book');
-
-	package MyApp::DBIC::Book;
-	use base qw/MyApp::DBIC/;
-
-	__PACKAGE__->table('books');
-	__PACKAGE__->add_columns(qw/bookID title edition isbn publisher year/);
-	__PACKAGE__->set_primary_key(qw/bookID/);
-	
-	__PACKAGE__->has_many('b2a' => 'MyApp::DBIC::Book2Author', 'bookID');
-
-	sub authors {
-	 my ($self) = @_;
-	 return MyApp::DBIC::Author->search(
-	   { 'b2a.bookID' => $self->bookID }, # WHERE clause
-	   { join => 'b2a' }); # join condition (part of search attrs)
-	}
-
-	# 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
+This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
+
+  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 ( $self, $attrs ) = @_;
+
+    $attrs->{foo} = 'bar' unless defined $attrs->{foo};
+
+    $self->next::method($attrs);
+
+    return $self;
+  }
+
+For more information about C<next::method>, look in the L<Class::C3> 
+documentation. See also L<DBIx::Class::Manual::Component> for more
+ways to write your own base classes to do this.
+
+People looking for ways to do "triggers" with DBIx::Class are probably
+just looking for this.
+
+=head2 Stringification
+
+Employ the standard stringification technique by using the C<overload>
+module.
+
+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 '""' => sub { shift->name}, fallback => 1;
+
+For more complex stringification, you can use an anonymous subroutine:
+
+  use overload '""' => sub { $_[0]->name . ", " .
+                             $_[0]->address }, fallback => 1;
+
+=head3 Stringification Example
+
+Suppose we have two tables: C<Product> and C<Category>. The table
+specifications are:
+
+  Product(id, Description, category)
+  Category(id, Description)
+
+C<category> is a foreign key into the Category table.
+
+If you have a Product object C<$obj> and write something like
+
+  print $obj->category
+
+things will not work as expected.
+
+To obtain, for example, the category description, you should add this
+method to the class defining the Category table:
+
+  use overload "" => sub {
+      my $self = shift;
+
+      return $self->Description;
+  }, 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->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 SQL::Translator::Parser::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('SQL::Translator::Parser::DBIx::Class');
+  $translator->producer('SQL::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 exercise for the reader.
+
+=head2 Schema versioning
+
+The following example shows simplistically how you might use DBIx::Class to
+deploy versioned schemas to your customers. The basic process is as follows:
+
+=over 4
+
+=item 1.
+
+Create a DBIx::Class schema
+
+=item 2.
+
+Save the schema
+
+=item 3.
+
+Deploy to customers
+
+=item 4.
+
+Modify schema to change functionality
+
+=item 5.
+
+Deploy update to customers
 
 =back
+
+=head3 Create a DBIx::Class schema
+
+This can either be done manually, or generated from an existing database as
+described under C<Schema import/export>.
+
+=head3 Save the schema
+
+Use C<sqlt> to transform your schema into an SQL script suitable for your
+customer's database. E.g. for MySQL:
+
+  sqlt --from SQL::Translator::Parser::DBIx::Class
+       --to MySQL
+       --DBIx::Class "MySchema.pm" > Schema1.mysql.sql
+
+If you need to target databases from multiple vendors, just generate an SQL
+script suitable for each. To support PostgreSQL too:
+
+  sqlt --from SQL::Translator::DBIx::Class
+       --to PostgreSQL
+       --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql
+
+=head3 Deploy to customers
+
+There are several ways you could deploy your schema. These are probably
+beyond the scope of this recipe, but might include:
+
+=over 4
+
+=item 1.
+
+Require customer to apply manually using their RDBMS.
+
+=item 2.
+
+Package along with your app, making database dump/schema update/tests
+all part of your install.
+
+=back
+
+=head3 Modify the schema to change functionality
+
+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:
+
+  sqlt --from SQL::Translator::DBIx::Class
+       --to MySQL
+       --DBIx::Class "Anything.pm" > Schema2.mysql.sql
+
+Next, use sqlt-diff to create an SQL script that will update the customer's
+database schema:
+
+  sqlt-diff --to MySQL Schema1=MySQL Schema2=MySQL > SchemaUpdate.mysql.sql
+
+=head3 Deploy update to customers
+
+The schema update can be deployed to customers using the same method as before.
+
+=head2 Setting limit dialect for SQL::Abstract::Limit
+
+In some cases, SQL::Abstract::Limit cannot determine the dialect of
+the remote SQL server by looking at the database handle. This is a
+common problem when using the DBD::JDBC, since the DBD-driver only
+know that in has a Java-driver available, not which JDBC driver the
+Java component has loaded.  This specifically sets the limit_dialect
+to Microsoft SQL-server (See more names in SQL::Abstract::Limit
+-documentation.
+
+  __PACKAGE__->storage->sql_maker->limit_dialect('mssql');
+
+The JDBC bridge is one way of getting access to a MSSQL server from a platform
+that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
+
+=head2 Setting quoting for the generated SQL. 
+
+If the database contains column names with spaces and/or reserved words, they
+need to be quoted in the SQL queries. This is done using:
+
+  __PACKAGE__->storage->sql_maker->quote_char([ qw/[ ]/] );
+  __PACKAGE__->storage->sql_maker->name_sep('.');
+
+The first sets the quote characters. Either a pair of matching
+brackets, or a C<"> or C<'>:
+  
+  __PACKAGE__->storage->sql_maker->quote_char('"');
+
+Check the documentation of your database for the correct quote
+characters to use. C<name_sep> needs to be set to allow the SQL
+generator to put the quotes the correct place.
+
+=head2 Overloading methods
+
+L<DBIx::Class> uses the L<Class::C3> package, which provides for redispatch of 
+method calls.  You have to use calls to C<next::method> to overload methods.  
+More information on using L<Class::C3> with L<DBIx::Class> can be found in 
+L<DBIx::Class::Manual::Component>.
+
+=head3 Changing one field whenever another changes
+
+For example, say that you have three columns, C<id>, C<number>, and 
+C<squared>.  You would like to make changes to C<number> and have
+C<squared> be automagically set to the value of C<number> squared.
+You can accomplish this by overriding C<store_column>:
+
+  sub store_column {
+    my ( $self, $name, $value ) = @_;
+    if ($name eq 'number') {
+      $self->squared($value * $value);
+    }
+    $self->next::method($name, $value);
+  }
+
+Note that the hard work is done by the call to C<next::method>, which
+redispatches your call to store_column in the superclass(es).
+
+=head3 Automatically creating related objects
+
+You might have a class C<Artist> which has many C<CD>s.  Further, if you
+want to create a C<CD> object every time you insert an C<Artist> object.
+You can accomplish this by overriding C<insert> on your objects:
+
+  sub insert {
+    my ( $self, @args ) = @_;
+    $self->next::method(@args);
+    $self->cds->new({})->fill_from_artist($self)->insert;
+    return $self;
+  }
+
+where C<fill_from_artist> is a method you specify in C<CD> which sets
+values in C<CD> based on the data in the C<Artist> object you pass in.
+
+=head2 Debugging DBIx::Class objects with Data::Dumper
+
+L<Data::Dumper> can be a very useful tool for debugging, but sometimes it can
+be hard to find the pertinent data in all the data it can generate.
+Specifically, if one naively tries to use it like so,
+
+  use Data::Dumper;
+
+  my $cd = $schema->resultset('CD')->find(1);
+  print Dumper($cd);
+
+several pages worth of data from the CD object's schema and result source will
+be dumped to the screen. Since usually one is only interested in a few column
+values of the object, this is not very helpful.
+
+Luckily, it is possible to modify the data before L<Data::Dumper> outputs
+it. Simply define a hook that L<Data::Dumper> will call on the object before
+dumping it. For example,
+
+  package My::DB::CD;
+
+  sub _dumper_hook {
+    $_[0] = bless {
+      %{ $_[0] },
+      result_source => undef,
+    }, ref($_[0]);
+  }
+
+  [...]
+
+  use Data::Dumper;
+
+  local $Data::Dumper::Freezer = '_dumper_hook';
+
+  my $cd = $schema->resultset('CD')->find(1);
+  print Dumper($cd);
+         # dumps $cd without its ResultSource
+
+If the structure of your schema is such that there is a common base class for
+all your table classes, simply put a method similar to C<_dumper_hook> in the
+base class and set C<$Data::Dumper::Freezer> to its name and L<Data::Dumper>
+will automagically clean up your data before printing it. See
+L<Data::Dumper/EXAMPLES> for more information.
+
+=head2 Retrieving a row object's Schema
+
+It is possible to get a Schema object from a row object like so:
+
+  my $schema = $cd->result_source->schema;
+  # use the schema as normal:
+  my $artist_rs = $schema->resultset('Artist'); 
+
+This can be useful when you don't want to pass around a Schema object to every
+method.
+
+=head2 Profiling
+
+When you enable L<DBIx::Class::Storage::DBI>'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
+mechanism:
+
+  package My::Profiler;
+  use strict;
+
+  use base 'DBIx::Class::Storage::Statistics';
+
+  use Time::HiRes qw(time);
+
+  my $start;
+
+  sub query_start {
+    my $self = shift();
+    my $sql = shift();
+    my $params = @_;
+
+    print "Executing $sql: ".join(', ', @params)."\n";
+    $start = time();
+  }
+
+  sub query_end {
+    my $self = shift();
+    my $sql = shift();
+    my @params = @_;
+
+    printf("Execution took %0.4f seconds.\n", time() - $start);
+    $start = undef;
+  }
+
+  1;
+
+You can then install that class as the debugging object:
+
+  __PACKAGE__->storage()->debugobj(new My::Profiler());
+  __PACKAGE__->storage()->debug(1);
+
+A more complicated example might involve storing each execution of SQL in an
+array:
+
+  sub query_end {
+    my $self = shift();
+    my $sql = shift();
+    my @params = @_;
+
+    my $elapsed = time() - $start;
+    push(@{ $calls{$sql} }, {
+        params => \@params,
+        elapsed => $elapsed
+    });
+  }
+
+You could then create average, high and low execution times for an SQL
+statement and dig down to see if certain parameters cause aberrant behavior.
+
+=head2 Getting the value of the primary key for the last database insert
+
+AKA getting last_insert_id
+
+If you are using PK::Auto, this is straightforward:
+
+  my $foo = $rs->create(\%blah);
+  # do more stuff
+  my $id = $foo->id; # foo->my_primary_key_field will also work.
+
+If you are not using autoincrementing primary keys, this will probably
+not work, but then you already know the value of the last primary key anyway.
+
+=head2 Dynamic Sub-classing DBIx::Class proxy classes 
+(AKA multi-class object inflation from one table) 
+ 
+L<DBIx::Class> classes are proxy classes, therefore some different
+techniques need to be employed for more than basic subclassing.  In
+this example we have a single user table that carries a boolean bit
+for admin.  We would like like to give the admin users
+objects(L<DBIx::Class::Row>) the same methods as a regular user but
+also special admin only methods.  It doesn't make sense to create two
+seperate proxy-class files for this.  We would be copying all the user
+methods into the Admin class.  There is a cleaner way to accomplish
+this.
+
+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,
+bless it if it's an admin object, and then return it.  See the example
+below:
+ 
+B<Schema Definition> 
+ 
+    package DB::Schema; 
+     
+    use base qw/DBIx::Class::Schema/; 
+ 
+    __PACKAGE__->load_classes(qw/User/); 
+ 
+ 
+B<Proxy-Class definitions> 
+ 
+    package DB::Schema::User; 
+     
+    use strict; 
+    use warnings; 
+    use base qw/DBIx::Class/; 
+     
+    ### Defined what our admin class is for ensure_class_loaded 
+    my $admin_class = __PACKAGE__ . '::Admin'; 
+     
+    __PACKAGE__->load_components(qw/Core/); 
+     
+    __PACKAGE__->table('users'); 
+     
+    __PACKAGE__->add_columns(qw/user_id   email    password  
+                                firstname lastname active 
+                                admin/); 
+     
+    __PACKAGE__->set_primary_key('user_id'); 
+     
+    sub inflate_result { 
+        my $self = shift;  
+        my $ret = $self->next::method(@_); 
+        if( $ret->admin ) {### If this is an admin rebless for extra functions  
+            $self->ensure_class_loaded( $admin_class ); 
+            bless $ret, $admin_class; 
+        } 
+        return $ret; 
+    } 
+     
+    sub hello { 
+        print "I am a regular user.\n"; 
+        return ; 
+    } 
+     
+     
+    package DB::Schema::User::Admin; 
+     
+    use strict; 
+    use warnings; 
+    use base qw/DB::Schema::User/; 
+     
+    sub hello 
+    { 
+        print "I am an admin.\n"; 
+        return; 
+    } 
+     
+    sub do_admin_stuff 
+    { 
+        print "I am doing admin stuff\n"; 
+        return ; 
+    } 
+ 
+B<Test File> test.pl 
+ 
+    use warnings; 
+    use strict; 
+    use DB::Schema; 
+     
+    my $user_data = { email    => 'someguy@place.com',  
+                      password => 'pass1',  
+                      admin    => 0 }; 
+                           
+    my $admin_data = { email    => 'someadmin@adminplace.com',  
+                       password => 'pass2',  
+                       admin    => 1 }; 
+                           
+    my $schema = DB::Schema->connection('dbi:Pg:dbname=test'); 
+     
+    $schema->resultset('User')->create( $user_data ); 
+    $schema->resultset('User')->create( $admin_data ); 
+     
+    ### Now we search for them 
+    my $user = $schema->resultset('User')->single( $user_data ); 
+    my $admin = $schema->resultset('User')->single( $admin_data ); 
+     
+    print ref $user, "\n"; 
+    print ref $admin, "\n"; 
+     
+    print $user->password , "\n"; # pass1 
+    print $admin->password , "\n";# pass2; inherited from User 
+    print $user->hello , "\n";# I am a regular user. 
+    print $admin->hello, "\n";# I am an admin. 
+ 
+    ### The statement below will NOT print 
+    print "I can do admin stuff\n" if $user->can('do_admin_stuff'); 
+    ### 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. Luckily this is also fairly easy using
+C<inflate_result>:
+
+  # Define a class which just returns the results as a hashref:
+  package My::HashRefInflator;
+
+  ## $me is the hashref of cols/data from the immediate resultsource
+  ## $prefetch is a deep hashref of all the data from the prefetched
+  ##   related sources.
+
+  sub mk_hash {
+     my ($me, $rest) = @_;
+
+     return { %$me, 
+        map { ($_ => mk_hash(@{$rest->{$_}})) } keys %$rest
+     };
+  }
+
+  sub inflate_result {
+     my ($self, $source, $me, $prefetch) = @_;
+     return mk_hash($me, $prefetch); 
+  }
+
+  # Change the object inflation to a hashref for just this resultset:
+  $rs->result_class('My::HashRefInflator');
+
+  my $datahashref = $rs->next;
+  foreach my $col (keys %$datahashref) {
+     if(!ref($datahashref->{$col})) {
+        # It's a plain value
+     }
+     elsif(ref($datahashref->{$col} eq 'HASH')) {
+        # It's a related value in a hashref
+     }
+  }
+
+=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