X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FManual%2FCookbook.pod;h=574a8e1eab1b4bd021b8a8aa94cb149b5dd96081;hb=d29565e0c545871399b0732e7781ea445e7d5b8c;hp=0552a037b9a8136424a635907f354d6721ada428;hpb=d2f3e87bbb670790a5572e1f7b92f33cc57585ab;p=dbsrgits%2FDBIx-Class-Historic.git

diff --git a/lib/DBIx/Class/Manual/Cookbook.pod b/lib/DBIx/Class/Manual/Cookbook.pod
index 0552a03..574a8e1 100644
--- a/lib/DBIx/Class/Manual/Cookbook.pod
+++ b/lib/DBIx/Class/Manual/Cookbook.pod
@@ -19,19 +19,8 @@ paged resultset, which will fetch only a defined number of records at a time:
 
   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 get a L<Data::Page> object for the
-resultset (suitable for use in e.g. a template) using the C<pager> method:
+You can get a L<Data::Page> object for the resultset (suitable for use
+in e.g. a template) using the C<pager> method:
 
   return $rs->pager();
 
@@ -68,6 +57,41 @@ This results in the following C<WHERE> clause:
 For more information on generating complex queries, see
 L<SQL::Abstract/WHERE CLAUSES>.
 
+=head2 Retrieve one and only one row from a resultset
+
+Sometimes you need only the first "top" row of a resultset. While this can be
+easily done with L<< $rs->first|DBIx::Class::ResultSet/first >>, it is suboptimal,
+as a full blown cursor for the resultset will be created and then immediately
+destroyed after fetching the first row object. 
+L<< $rs->single|DBIx::Class::ResultSet/single >> is
+designed specifically for this case - it will grab the first returned result
+without even instantiating a cursor. 
+
+Before replacing all your calls to C<first()> with C<single()> please observe the 
+following CAVEATS:
+
+=over
+
+=item *
+While single() takes a search condition just like search() does, it does
+_not_ accept search attributes. However one can always chain a single() to
+a search():
+
+  my $top_cd = $cd_rs -> search({}, { order_by => 'rating' }) -> single;
+
+
+=item *
+Since single() is the engine behind find(), it is designed to fetch a
+single row per database query. Thus a warning will be issued when the
+underlying SELECT returns more than one row. Sometimes however this usage
+is valid: i.e. we have an arbitrary number of cd's but only one of them is
+at the top of the charts at any given time. If you know what you are doing,
+you can silence the warning by explicitly limiting the resultset size:
+
+  my $top_cd = $cd_rs -> search ({}, { order_by => 'rating', rows => 1 }) -> single;
+
+=back
+
 =head2 Arbitrary SQL through a custom ResultSource
 
 Sometimes you have to run arbitrary SQL because your query is too complex
@@ -81,7 +105,7 @@ 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;
+  package My::Schema::Result::User;
   
   use base qw/DBIx::Class/;
   
@@ -106,7 +130,7 @@ you have to add to your User class:
   SQL 
 
   # Finally, register your new ResultSource with your Schema
-  My::Schema->register_source( 'UserFriendsComplex' => $new_source );
+  My::Schema->register_extra_source( 'UserFriendsComplex' => $new_source );
 
 Next, you can execute your complex query using bind parameters like this:
 
@@ -116,7 +140,36 @@ Next, you can execute your complex query using bind parameters like this:
     }
   ) ];
   
-... and you'll get back a perfect L<DBIx::Class::ResultSet>.
+... and you'll get back a perfect L<DBIx::Class::ResultSet> (except, of course,
+that you cannot modify the rows it contains, ie. cannot call L</update>,
+L</delete>, ...  on it).
+
+If you prefer to have the definitions of these custom ResultSources in separate
+files (instead of stuffing all of them into the same resultset class), you can
+achieve the same with subclassing the resultset class and defining the
+ResultSource there:
+
+  package My::Schema::Result::UserFriendsComplex;
+
+  use My::Schema::Result::User;
+  use base qw/My::Schema::Result::User/;
+
+  __PACKAGE__->table('dummy');  # currently must be called before anything else
+
+  # 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!
+  __PACKAGE__->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
+
+TIMTOWDI.
 
 =head2 Using specific columns
 
@@ -184,30 +237,50 @@ any of your aliases using either of these:
 
 =head2 SELECT DISTINCT with multiple columns
 
-  my $rs = $schema->resultset('Foo')->search(
+  my $rs = $schema->resultset('Artist')->search(
     {},
     {
-      select => [
-        { distinct => [ $source->columns ] }
-      ],
-      as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
+      columns => [ qw/artistid name rank/ ],
+      distinct => 1
+    } 
+  );
+
+  my $rs = $schema->resultset('Artist')->search(
+    {},
+    {
+      columns => [ qw/artistid name rank/ ],
+      group_by => [ qw/artistid name rank/ ],
     }
   );
 
-  my $count = $rs->next->get_column('count');
+  # Equivalent SQL:
+  # SELECT me.artistid, me.name, me.rank
+  # FROM artist me
+  # GROUP BY artistid, name, rank
 
 =head2 SELECT COUNT(DISTINCT colname)
 
-  my $rs = $schema->resultset('Foo')->search(
+  my $rs = $schema->resultset('Artist')->search(
+    {},
+    {
+      columns => [ qw/name/ ],
+      distinct => 1
+    }
+  );
+
+  my $rs = $schema->resultset('Artist')->search(
     {},
     {
-      select => [
-        { count => { distinct => 'colname' } }
-      ],
-      as => [ 'count' ]
+      columns => [ qw/name/ ],
+      group_by => [ qw/name/ ],
     }
   );
 
+  my $count = $rs->count;
+
+  # Equivalent SQL:
+  # SELECT COUNT( DISTINCT( me.name ) ) FROM artist me 
+
 =head2 Grouping results
 
 L<DBIx::Class> supports C<GROUP BY> as follows:
@@ -216,21 +289,73 @@ L<DBIx::Class> supports C<GROUP BY> as follows:
     {},
     {
       join     => [qw/ cds /],
-      select   => [ 'name', { count => 'cds.cdid' } ],
+      select   => [ 'name', { count => 'cds.id' } ],
       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 )
+  # SELECT name, COUNT( cd.id ) FROM artist
+  # LEFT JOIN cd ON artist.id = cd.artist
   # 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 >).
 
+=head2 Subqueries (EXPERIMENTAL)
+
+You can write subqueries relatively easily in DBIC.
+
+  my $inside_rs = $schema->resultset('Artist')->search({
+    name => [ 'Billy Joel', 'Brittany Spears' ],
+  });
+
+  my $rs = $schema->resultset('CD')->search({
+    artist_id => { 'IN' => $inside_rs->get_column('id')->as_query },
+  });
+
+The usual operators ( =, !=, IN, NOT IN, etc) are supported.
+
+B<NOTE>: You have to explicitly use '=' when doing an equality comparison.
+The following will B<not> work:
+
+  my $rs = $schema->resultset('CD')->search({
+    artist_id => $inside_rs->get_column('id')->as_query,
+  });
+
+=head3 Support
+
+Subqueries are supported in the where clause (first hashref), and in the
+from, select, and +select attributes.
+
+=head3 Correlated subqueries
+
+  my $cdrs = $schema->resultset('CD');
+  my $rs = $cdrs->search({
+    year => {
+      '=' => $cdrs->search(
+        { artistid => { '=' => \'me.artistid' } },
+        { alias => 'inner' }
+      )->get_column('year')->max_rs->as_query,
+    },
+  });
+
+That creates the following SQL:
+
+  SELECT me.cdid, me.artist, me.title, me.year, me.genreid, me.single_track
+    FROM cd me
+   WHERE year = (
+      SELECT MAX(inner.year)
+        FROM cd inner
+       WHERE artistid = me.artistid
+      )
+
+=head3 EXPERIMENTAL
+
+Please note that subqueries are considered an experimental feature.
+
 =head2 Predefined searches
 
 You can write your own L<DBIx::Class::ResultSet> class by inheriting from it
@@ -255,8 +380,15 @@ and define often used searches as methods:
 To use your resultset, first tell DBIx::Class to create an instance of it
 for you, in your My::DBIC::Schema::CD class:
 
+  # class definition as normal
+  __PACKAGE__->load_components(qw/ Core /);
+  __PACKAGE__->table('cd');
+
+  # tell DBIC to use the custom ResultSet class
   __PACKAGE__->resultset_class('My::DBIC::ResultSet::CD');
 
+Note that C<resultset_class> must be called after C<load_components> and C<table>, or you will get errors about missing methods.
+
 Then call your new method in your code:
 
    my $ordered_cds = $schema->resultset('CD')->search_cds_ordered();
@@ -305,7 +437,7 @@ a particular artist name:
       'artist.name' => 'Bob Marley'    
     },
     {
-      join => [qw/artist/], # join the artist table
+      join => 'artist', # join the artist table
     }
   );
 
@@ -322,7 +454,7 @@ it in your C<order_by> attribute:
       'artist.name' => 'Bob Marley'
     },
     {
-      join     => [qw/ artist /],
+      join     => 'artist',
       order_by => [qw/ artist.name /]
     }
   );
@@ -363,9 +495,9 @@ This allows you to fetch results from related tables in advance:
       'artist.name' => 'Bob Marley'
     },
     {
-      join     => [qw/ artist /],
+      join     => 'artist',
       order_by => [qw/ artist.name /],
-      prefetch => [qw/ artist /] # return artist data too!
+      prefetch => 'artist' # return artist data too!
     }
   );
 
@@ -385,13 +517,38 @@ 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!
 
+=head2 Multiple joins
+
+In the examples above, the C<join> attribute was a scalar.  If you
+pass an array reference instead, you can join to multiple tables.  In
+this example, we want to limit the search further, using
+C<LinerNotes>:
+
+  # Relationships defined elsewhere:
+  # CD->belongs_to('artist' => 'Artist');
+  # CD->has_one('liner_notes' => 'LinerNotes', 'cd');
+  my $rs = $schema->resultset('CD')->search(
+    {
+      'artist.name' => 'Bob Marley'
+      'liner_notes.notes' => { 'like', '%some text%' },
+    },
+    {
+      join     => [qw/ artist liner_notes /],
+      order_by => [qw/ artist.name /],
+    }
+  );
+
+  # Equivalent SQL:
+  # SELECT cd.*, artist.*, liner_notes.* FROM cd
+  # JOIN artist ON cd.artist = artist.id
+  # JOIN liner_notes ON cd.id = liner_notes.cd
+  # WHERE artist.name = 'Bob Marley'
+  # ORDER BY artist.name
+
 =head2 Multi-step joins
 
 Sometimes you want to join more than one relationship deep. In this example,
@@ -415,8 +572,8 @@ contain a specific string:
 
   # Equivalent SQL:
   # SELECT artist.* FROM artist
-  # JOIN ( cd ON artist.id = cd.artist )
-  # JOIN ( liner_notes ON cd.id = liner_notes.cd )
+  # LEFT JOIN cd ON artist.id = cd.artist
+  # LEFT 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
@@ -442,15 +599,42 @@ notes:
 
   # 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 )
+  # LEFT JOIN cd ON artist.id = cd.artist
+  # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
+  # LEFT JOIN author ON author.id = liner_notes.author
   # WHERE liner_notes.notes LIKE '%some text%'
   # AND author.name = 'A. Writer'
 
+=head2 Multi-step and multiple joins
+
+With various combinations of array and hash references, you can join
+tables in any combination you desire.  For example, to join Artist to
+CD and Concert, and join CD to LinerNotes:
+
+  # Relationships defined elsewhere:
+  # Artist->has_many('concerts' => 'Concert', 'artist');
+
+  my $rs = $schema->resultset('Artist')->search(
+    { },
+    {
+      join => [
+        {
+          cds => 'liner_notes'
+        },
+        'concerts'
+      ],
+    }
+  );
+
+  # Equivalent SQL:
+  # SELECT artist.* FROM artist
+  # LEFT JOIN cd ON artist.id = cd.artist
+  # LEFT JOIN liner_notes ON cd.id = liner_notes.cd
+  # LEFT JOIN concert ON artist.id = concert.artist
+
 =head2 Multi-step prefetch
 
-From 0.04999_05 onwards, C<prefetch> can be nested more than one relationship
+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(
@@ -464,8 +648,8 @@ deep using the same syntax as a multi-step join:
 
   # Equivalent SQL:
   # SELECT tag.*, cd.*, artist.* FROM tag
-  # JOIN cd ON tag.cd = cd.cdid
-  # JOIN artist ON cd.artist = artist.artistid
+  # JOIN cd ON tag.cd = cd.id
+  # JOIN artist ON cd.artist = artist.id
 
 Now accessing our C<cd> and C<artist> relationships does not need additional
 SQL statements:
@@ -490,8 +674,7 @@ method.
 
 AKA getting last_insert_id
 
-If you are using PK::Auto (which is a core component as of 0.07), this is 
-straightforward:
+Thanks to the core component PK::Auto, this is straightforward:
 
   my $foo = $rs->create(\%blah);
   # do more stuff
@@ -506,7 +689,7 @@ 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):
+like this (replace C<name> with the column/method of your choice):
 
   use overload '""' => sub { shift->name}, fallback => 1;
 
@@ -550,6 +733,48 @@ Just use C<find_or_new> instead, then check C<in_storage>:
     # do whatever else you wanted if it was a new row
   }
 
+=head2 Static sub-classing DBIx::Class result classes 
+
+AKA adding additional relationships/methods/etc. to a model for a
+specific usage of the (shared) model.
+
+B<Schema definition> 
+ 
+    package My::App::Schema; 
+     
+    use base DBIx::Class::Schema; 
+
+    # load subclassed classes from My::App::Schema::Result/ResultSet
+    __PACKAGE__->load_namespaces;
+
+    # load classes from shared model
+    load_classes({
+        'My::Shared::Model::Result' => [qw/
+            Foo
+            Bar
+        /]});
+
+    1;
+ 
+B<Result-Subclass definition> 
+ 
+    package My::App::Schema::Result::Baz;
+     
+    use strict; 
+    use warnings; 
+    use base My::Shared::Model::Result::Baz; 
+    
+    # WARNING: Make sure you call table() again in your subclass,
+    # otherwise DBIx::Class::ResultSourceProxy::Table will not be called
+    # and the class name is not correctly registered as a source
+    __PACKAGE__->table('baz'); 
+     
+    sub additional_method { 
+        return "I'm an additional method only needed by this app"; 
+    }
+
+    1;
+     
 =head2 Dynamic Sub-classing DBIx::Class proxy classes 
 
 AKA multi-class object inflation from one table
@@ -573,16 +798,18 @@ below:
  
 B<Schema Definition> 
  
-    package DB::Schema; 
+    package My::Schema; 
      
     use base qw/DBIx::Class::Schema/; 
  
-    __PACKAGE__->load_classes(qw/User/); 
+    __PACKAGE__->load_namespaces;
+
+    1;
  
  
 B<Proxy-Class definitions> 
  
-    package DB::Schema::User; 
+    package My::Schema::Result::User; 
      
     use strict; 
     use warnings; 
@@ -615,13 +842,15 @@ B<Proxy-Class definitions>
         print "I am a regular user.\n"; 
         return ; 
     } 
+    
+    1;
+
      
-     
-    package DB::Schema::User::Admin; 
+    package My::Schema::Result::User::Admin; 
      
     use strict; 
     use warnings; 
-    use base qw/DB::Schema::User/; 
+    use base qw/My::Schema::Result::User/; 
      
     sub hello 
     { 
@@ -633,13 +862,15 @@ B<Proxy-Class definitions>
     { 
         print "I am doing admin stuff\n"; 
         return ; 
-    } 
+    }
+
+    1;
  
 B<Test File> test.pl 
  
     use warnings; 
     use strict; 
-    use DB::Schema; 
+    use My::Schema; 
      
     my $user_data = { email    => 'someguy@place.com',  
                       password => 'pass1',  
@@ -649,7 +880,7 @@ B<Test File> test.pl
                        password => 'pass2',  
                        admin    => 1 }; 
                            
-    my $schema = DB::Schema->connection('dbi:Pg:dbname=test'); 
+    my $schema = My::Schema->connection('dbi:Pg:dbname=test'); 
      
     $schema->resultset('User')->create( $user_data ); 
     $schema->resultset('User')->create( $admin_data ); 
@@ -671,7 +902,7 @@ B<Test File> test.pl
     ### 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
+=head2 Skip row 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
@@ -684,17 +915,22 @@ To do this simply use L<DBIx::Class::ResultClass::HashRefInflator>.
  $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
  
  my $hash_ref = $rs->find(1);
-  
+
 Wasn't that easy?
-  
+
+Beware, changing the Result class using
+L<DBIx::Class::ResultSet/result_class> will replace any existing class
+completely including any special components loaded using
+load_components, eg L<DBIx::Class::InflateColumn::DateTime>.
+
 =head2 Get raw data for blindingly fast results
 
 If the L<HashRefInflator|DBIx::Class::ResultClass::HashRefInflator> 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
+exactly as they come out of the database with none of the convenience methods
 wrapped round them.
 
-This is used like so:-
+This is used like so:
 
   my $cursor = $rs->cursor
   while (my @vals = $cursor->next) {
@@ -702,13 +938,13 @@ This is used like so:-
   }
 
 You will need to map the array offsets to particular columns (you can
-use the I<select> attribute of C<search()> to force ordering).
+use the L<DBIx::Class::ResultSet/select> attribute of L<DBIx::Class::ResultSet/search> to force ordering).
 
 =head1 RESULTSET OPERATIONS
 
 =head2 Getting Schema from a ResultSet
 
-To get the schema object from a result set, do the following:
+To get the L<DBIx::Class::Schema> object from a ResultSet, do the following:
 
  $rs->result_source->schema
 
@@ -763,42 +999,64 @@ This will cause the following SQL statement to be run:
 Which will of course only work if your database supports this function.
 See L<DBIx::Class::ResultSetColumn> for more documentation.
 
+=head2 Creating a result set from a set of rows
+
+Sometimes you have a (set of) row objects that you want to put into a 
+resultset without the need to hit the DB again. You can do that by using the
+L<set_cache|DBIx::Class::Resultset/set_cache> method:
+
+ my @uploadable_groups;
+ while (my $group = $groups->next) {
+   if ($group->can_upload($self)) {
+     push @uploadable_groups, $group;
+   }
+ }
+ my $new_rs = $self->result_source->resultset;
+ $new_rs->set_cache(\@uploadable_groups);
+ return $new_rs;
+
+
 =head1 USING RELATIONSHIPS
 
 =head2 Create a new row in a related table
 
-  my $book->create_related('author', { name => 'Fred'});
+  my $author = $book->create_related('author', { name => 'Fred'});
 
 =head2 Search in a related table
 
 Only searches for books named 'Titanic' by the author in $author.
 
-  my $author->search_related('books', { name => 'Titanic' });
+  my $books_rs = $author->search_related('books', { name => 'Titanic' });
 
 =head2 Delete data in a related table
 
 Deletes only the book named Titanic by the author in $author.
 
-  my $author->delete_related('books', { name => 'Titanic' });
+  $author->delete_related('books', { name => 'Titanic' });
 
 =head2 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.
+To order C<< $book->pages >> by descending page_number, create the relation
+as follows:
 
-  Book->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
+  __PACKAGE__->has_many('pages' => 'Page', 'book', { order_by => \'page_number DESC'} );
+
+=head2 Filtering a relationship result set
+
+If you want to get a filtered result set, you can just add add to $attr as follows:
+
+ __PACKAGE__->has_many('pages' => 'Page', 'book', { where => { scrap => 0 } } );
 
 =head2 Many-to-many relationships
 
 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';
+  use base 'DBIx::Class';
+  __PACKAGE__->load_components('Core');
   __PACKAGE__->table('user');
   __PACKAGE__->add_columns(qw/id name/);
   __PACKAGE__->set_primary_key('id');
@@ -806,7 +1064,8 @@ This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_man
   __PACKAGE__->many_to_many('addresses' => 'user_address', 'address');
 
   package My::UserAddress;
-  use base 'My::DB';
+  use base 'DBIx::Class';
+  __PACKAGE__->load_components('Core');
   __PACKAGE__->table('user_address');
   __PACKAGE__->add_columns(qw/user address/);
   __PACKAGE__->set_primary_key(qw/user address/);
@@ -814,7 +1073,8 @@ This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_man
   __PACKAGE__->belongs_to('address' => 'My::Address');
 
   package My::Address;
-  use base 'My::DB';
+  use base 'DBIx::Class';
+  __PACKAGE__->load_components('Core');
   __PACKAGE__->table('address');
   __PACKAGE__->add_columns(qw/id street town area_code country/);
   __PACKAGE__->set_primary_key('id');
@@ -824,6 +1084,98 @@ This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_man
   $rs = $user->addresses(); # get all addresses for a user
   $rs = $address->users(); # get all users for an address
 
+=head2 Relationships across DB schemas
+
+Mapping relationships across L<DB schemas|DBIx::Class::Manual::Glossary/DB schema>
+is easy as long as the schemas themselves are all accessible via the same DBI
+connection. In most cases, this means that they are on the same database host
+as each other and your connecting database user has the proper permissions to them.
+
+To accomplish this one only needs to specify the DB schema name in the table
+declaration, like so...
+
+  package MyDatabase::Main::Artist;
+  use base qw/DBIx::Class/;
+  __PACKAGE__->load_components(qw/PK::Auto Core/);
+  
+  __PACKAGE__->table('database1.artist'); # will use "database1.artist" in FROM clause
+  
+  __PACKAGE__->add_columns(qw/ artistid name /);
+  __PACKAGE__->set_primary_key('artistid');
+  __PACKAGE__->has_many('cds' => 'MyDatabase::Main::Cd');
+
+  1;
+
+Whatever string you specify there will be used to build the "FROM" clause in SQL
+queries.
+
+The big drawback to this is you now have DB schema names hardcoded in your
+class files. This becomes especially troublesome if you have multiple instances
+of your application to support a change lifecycle (e.g. DEV, TEST, PROD) and
+the DB schemas are named based on the environment (e.g. database1_dev).
+
+However, one can dynamically "map" to the proper DB schema by overriding the
+L<connection|DBIx::Class::Schama/connection> method in your Schema class and
+building a renaming facility, like so:
+
+  package MyDatabase::Schema;
+  use Moose;
+  
+  extends 'DBIx::Class::Schema';
+  
+  around connection => sub {
+    my ( $inner, $self, $dsn, $username, $pass, $attr ) = ( shift, @_ );
+   
+    my $postfix = delete $attr->{schema_name_postfix};
+    
+    $inner->(@_);
+    
+    if ( $postfix ) {
+        $self->append_db_name($postfix);
+    }
+  };
+
+  sub append_db_name {
+    my ( $self, $postfix ) = @_;
+    
+    my @sources_with_db 
+        = grep 
+            { $_->name =~ /^\w+\./mx } 
+            map 
+                { $self->source($_) } 
+                $self->sources;
+    
+    foreach my $source (@sources_with_db) {
+        my $name = $source->name;
+        $name =~ s{^(\w+)\.}{${1}${postfix}\.}mx;
+        
+        $source->name($name);
+    }
+  }
+
+  1;
+
+By overridding the L<connection|DBIx::Class::Schama/connection>
+method and extracting a custom option from the provided \%attr hashref one can
+then simply iterate over all the Schema's ResultSources, renaming them as
+needed.
+
+To use this facility, simply add or modify the \%attr hashref that is passed to 
+L<connection|DBIx::Class::Schama/connect>, as follows:
+
+  my $schema 
+    = MyDatabase::Schema->connect(
+      $dsn, 
+      $user, 
+      $pass,
+      {
+        schema_name_postfix => '_dev'
+        # ... Other options as desired ... 
+      })
+
+Obviously, one could accomplish even more advanced mapping via a hash map or a
+callback routine.
+
 =head1 TRANSACTIONS
 
 As of version 0.04001, there is improved transaction support in
@@ -841,7 +1193,7 @@ example of the recommended way to use it:
     $genus->add_to_species({ name => 'troglodyte' });
     $genus->wings(2);
     $genus->update;
-    $schema->txn_do($coderef2); # Can have a nested transaction
+    $schema->txn_do($coderef2); # Can have a nested transaction. Only the outer will actualy commit
     return $genus->species;
   };
 
@@ -874,7 +1226,8 @@ L<DBIx::Class::Schema> and associated sources by examining the database.
 The recommend way of achieving this is to use the 
 L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> method:
 
-  perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
+  perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:./lib \
+    -e 'make_schema_at("My::Schema", { debug => 1 }, [ "dbi:Pg:dbname=foo","postgres" ])'
 
 This will create a tree of files rooted at C<./lib/My/Schema/> containing
 source definitions for all the tables found in the C<foo> database.
@@ -920,13 +1273,119 @@ of the schema, plus scripts to convert from version 0.1 to 0.2. This
 requires that the files for 0.1 as created above are available in the
 given directory to diff against.
 
+=head2 Select from dual
+
+Dummy tables are needed by some databases to allow calling functions
+or expressions that aren't based on table content, for examples of how
+this applies to various database types, see:
+L<http://troels.arvin.dk/db/rdbms/#other-dummy_table>.
+
+Note: If you're using Oracles dual table don't B<ever> do anything
+other than a select, if you CRUD on your dual table you *will* break
+your database.
+
+Make a table class as you would for any other table
+                                                                               
+  package MyAppDB::Dual;
+  use strict;
+  use warnings;
+  use base 'DBIx::Class';
+  __PACKAGE__->load_components("Core");
+  __PACKAGE__->table("Dual");
+  __PACKAGE__->add_columns(
+    "dummy",
+    { data_type => "VARCHAR2", is_nullable => 0, size => 1 },
+  );
+ 
+Once you've loaded your table class select from it using C<select>
+and C<as> instead of C<columns>
+ 
+  my $rs = $schema->resultset('Dual')->search(undef,
+    { select => [ 'sydate' ],
+      as     => [ 'now' ]
+    },
+  );
+ 
+All you have to do now is be careful how you access your resultset, the below
+will not work because there is no column called 'now' in the Dual table class
+ 
+  while (my $dual = $rs->next) {
+    print $dual->now."\n";
+  }
+  # Can't locate object method "now" via package "MyAppDB::Dual" at headshot.pl line 23.
+ 
+You could of course use 'dummy' in C<as> instead of 'now', or C<add_columns> to
+your Dual class for whatever you wanted to select from dual, but that's just
+silly, instead use C<get_column>
+ 
+  while (my $dual = $rs->next) {
+    print $dual->get_column('now')."\n";
+  }
+ 
+Or use C<cursor>
+ 
+  my $cursor = $rs->cursor;
+  while (my @vals = $cursor->next) {
+    print $vals[0]."\n";
+  }
+
+In case you're going to use this "trick" together with L<DBIx::Class::Schema/deploy> or
+L<DBIx::Class::Schema/create_ddl_dir> a table called "dual" will be created in your
+current schema. This would overlap "sys.dual" and you could not fetch "sysdate" or
+"sequence.nextval" anymore from dual. To avoid this problem, just tell
+L<SQL::Translator> to not create table dual:
+
+    my $sqlt_args = {
+        add_drop_table => 1,
+        parser_args    => { sources => [ grep $_ ne 'Dual', schema->sources ] },
+    };
+    $schema->create_ddl_dir( [qw/Oracle/], undef, './sql', undef, $sqlt_args );
+ 
+Or use L<DBIx::Class::ResultClass::HashRefInflator>
+ 
+  $rs->result_class('DBIx::Class::ResultClass::HashRefInflator');
+  while ( my $dual = $rs->next ) {
+    print $dual->{now}."\n";
+  }
+ 
+Here are some example C<select> conditions to illustrate the different syntax
+you could use for doing stuff like 
+C<oracles.heavily(nested(functions_can('take', 'lots'), OF), 'args')>
+ 
+  # get a sequence value
+  select => [ 'A_SEQ.nextval' ],
+ 
+  # get create table sql
+  select => [ { 'dbms_metadata.get_ddl' => [ "'TABLE'", "'ARTIST'" ]} ],
+ 
+  # get a random num between 0 and 100
+  select => [ { "trunc" => [ { "dbms_random.value" => [0,100] } ]} ],
+ 
+  # what year is it?
+  select => [ { 'extract' => [ \'year from sysdate' ] } ],
+ 
+  # do some math
+  select => [ {'round' => [{'cos' => [ \'180 * 3.14159265359/180' ]}]}],
+ 
+  # which day of the week were you born on?
+  select => [{'to_char' => [{'to_date' => [ "'25-DEC-1980'", "'dd-mon-yyyy'" ]}, "'day'"]}],
+ 
+  # select 16 rows from dual
+  select   => [ "'hello'" ],
+  as       => [ 'world' ],
+  group_by => [ 'cube( 1, 2, 3, 4 )' ],
+ 
+ 
+
 =head2 Adding Indexes And Functions To Your SQL
 
 Often you will want indexes on columns on your table to speed up searching. To
 do this, create a method called C<sqlt_deploy_hook> in the relevant source 
-class:
+class (refer to the advanced 
+L<callback system|DBIx::Class::ResultSource/sqlt_deploy_callback> if you wish
+to share a hook between multiple sources):
 
- package My::Schema::Artist;
+ package My::Schema::Result::Artist;
 
  __PACKAGE__->table('artist');
  __PACKAGE__->add_columns(id => { ... }, name => { ... })
@@ -958,9 +1417,11 @@ created:
    $sqlt_schema->drop_table('table_name');
  }
 
-You could also add views or procedures to the output using 
-L<SQL::Translator::Schema/add_view> or 
-L<SQL::Translator::Schema/add_procedure>.
+You could also add views, procedures or triggers to the output using
+L<SQL::Translator::Schema/add_view>,
+L<SQL::Translator::Schema/add_procedure> or
+L<SQL::Translator::Schema/add_trigger>.
+
 
 =head2 Schema versioning
 
@@ -1029,7 +1490,7 @@ B<Deploy update to customers>
 
 Add the L<DBIx::Class::Schema::Versioned> schema component to your
 Schema class. This will add a new table to your database called
-C<SchemaVersions> which will keep track of which version is installed
+C<dbix_class_schema_vesion> which will keep track of which version is installed
 and warn if the user trys to run a newer schema version than the
 database thinks it has.
 
@@ -1054,7 +1515,7 @@ characters to use. C<name_sep> needs to be set to allow the SQL
 generator to put the quotes the correct place.
 
 In most cases you should set these as part of the arguments passed to 
-L<DBIx::Class::Schema/conect>:
+L<DBIx::Class::Schema/connect>:
 
  my $schema = My::Schema->connect(
   'dbi:mysql:my_db',
@@ -1084,6 +1545,44 @@ that Microsoft doesn't deliver native client libraries for. (e.g. Linux)
 The limit dialect can also be set at connect time by specifying a 
 C<limit_dialect> key in the final hash as shown above.
 
+=head2 Working with PostgreSQL array types
+
+You can also assign values to PostgreSQL array columns by passing array
+references in the C<\%columns> (C<\%vals>) hashref of the
+L<DBIx::Class::ResultSet/create> and L<DBIx::Class::Row/update> family of
+methods:
+
+  $resultset->create({
+    numbers => [1, 2, 3]
+  });
+
+  $row->update(
+    {
+      numbers => [1, 2, 3]
+    },
+    {
+      day => '2008-11-24'
+    }
+  );
+
+In conditions (eg. C<\%cond> in the L<DBIx::Class::ResultSet/search> family of
+methods) you cannot directly use array references (since this is interpreted as
+a list of values to be C<OR>ed), but you can use the following syntax to force
+passing them as bind values:
+
+  $resultset->search(
+    {
+      numbers => \[ '= ?', [numbers => [1, 2, 3]] ]
+    }
+  );
+
+See L<SQL::Abstract/array_datatypes> and L<SQL::Abstract/Literal SQL with
+placeholders and bind values (subqueries)> for more explanation. Note that
+L<DBIx::Class> sets L<SQL::Abstract/bindtype> to C<columns>, so you must pass
+the bind values (the C<[1, 2, 3]> arrayref in the above example) wrapped in
+arrayrefs together with the column name, like this: C<< [column_name => value]
+>>.
+
 =head1 BOOTSTRAPPING/MIGRATING 
 
 =head2 Easy migration from class-based to schema-based setup
@@ -1337,5 +1836,96 @@ 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.
 You might want to check out L<DBIx::Class::QueryLog> as well.
 
+=head1 STARTUP SPEED
+
+L<DBIx::Class|DBIx::Class> programs can have a significant startup delay
+as the ORM loads all the relevant classes. This section examines
+techniques for reducing the startup delay.
+
+These tips are are listed in order of decreasing effectiveness - so the
+first tip, if applicable, should have the greatest effect on your
+application.
+
+=head2 Statically Define Your Schema
+
+If you are using
+L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to build the
+classes dynamically based on the database schema then there will be a
+significant startup delay.
+
+For production use a statically defined schema (which can be generated
+using L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to dump
+the database schema once - see
+L<make_schema_at|DBIx::Class::Schema::Loader/make_schema_at> and
+L<dump_directory|DBIx::Class::Schema::Loader/dump_directory> for more
+details on creating static schemas from a database).
+
+=head2 Move Common Startup into a Base Class
+
+Typically L<DBIx::Class> result classes start off with
+
+    use base qw/DBIx::Class/;
+    __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
+
+If this preamble is moved into a common base class:-
+
+    package MyDBICbase;
+    
+    use base qw/DBIx::Class/;
+    __PACKAGE__->load_components(qw/InflateColumn::DateTime Core/);
+    1;
+
+and each result class then uses this as a base:-
+
+    use base qw/MyDBICbase/;
+
+then the load_components is only performed once, which can result in a
+considerable startup speedup for schemas with many classes.
+
+=head2 Explicitly List Schema Result Classes
+
+The schema class will normally contain
+
+    __PACKAGE__->load_classes();
+
+to load the result classes. This will use L<Module::Find|Module::Find>
+to find and load the appropriate modules. Explicitly defining the
+classes you wish to load will remove the overhead of
+L<Module::Find|Module::Find> and the related directory operations:-
+
+    __PACKAGE__->load_classes(qw/ CD Artist Track /);
+
+If you are instead using the L<load_namespaces|DBIx::Class::Schema/load_namespaces>
+syntax to load the appropriate classes there is not a direct alternative
+avoiding L<Module::Find|Module::Find>.
+
+=head1 MEMORY USAGE
+
+=head2 Cached statements
+
+L<DBIx::Class> normally caches all statements with L<< prepare_cached()|DBI/prepare_cached >>.
+This is normally a good idea, but if too many statements are cached, the database may use too much
+memory and may eventually run out and fail entirely.  If you suspect this may be the case, you may want
+to examine DBI's L<< CachedKids|DBI/CachedKidsCachedKids_(hash_ref) >> hash:
+
+    # print all currently cached prepared statements
+    print for keys %{$schema->storage->dbh->{CachedKids}};
+    # get a count of currently cached prepared statements
+    my $count = scalar keys %{$schema->storage->dbh->{CachedKids}};
+
+If it's appropriate, you can simply clear these statements, automatically deallocating them in the
+database:
+
+    my $kids = $schema->storage->dbh->{CachedKids};
+    delete @{$kids}{keys %$kids} if scalar keys %$kids > 100;
+
+But what you probably want is to expire unused statements and not those that are used frequently.
+You can accomplish this with L<Tie::Cache> or L<Tie::Cache::LRU>:
+
+    use Tie::Cache;
+    use DB::Main;
+    my $schema = DB::Main->connect($dbi_dsn, $user, $pass, {
+        on_connect_do => sub { tie %{shift->_dbh->{CachedKids}}, 'Tie::Cache', 100 },
+    });
 
 =cut