X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FManual%2FCookbook.pod;h=081a4d0dea2d2f6a1c93ff9548dd0437c6f9af7d;hb=4c24816137de09c629fcd3da41b7626d50cc13f6;hp=715c8f85e61a61f6878f271e1fc9f6bd5e0aac14;hpb=5e8b1b2adbc7b67dc7948a41354e36ce0c7998c6;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Manual/Cookbook.pod b/lib/DBIx/Class/Manual/Cookbook.pod
index 715c8f8..081a4d0 100644
--- a/lib/DBIx/Class/Manual/Cookbook.pod
+++ b/lib/DBIx/Class/Manual/Cookbook.pod
@@ -138,6 +138,8 @@ any of your aliases using either of these:
     }
   );
 
+  my $count = $rs->next->get_column('count');
+
 =head3 SELECT COUNT(DISTINCT colname)
 
   my $rs = $schema->resultset('Foo')->search(
@@ -169,6 +171,57 @@ L<DBIx::Class> supports C<GROUP BY> as follows:
   # LEFT JOIN cd cds ON ( cds.artist = me.artistid )
   # GROUP BY name
 
+=head3 Predefined searches
+
+You can write your own 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
 
 You can use the C<join> attribute to allow searching on, or sorting your
@@ -362,7 +415,7 @@ example of the recommended way to use it:
     $genus->add_to_species({ name => 'troglodyte' });
     $genus->wings(2);
     $genus->update;
-    $schema->txn_do($code, $genus); # Can have a nested transation
+    $schema->txn_do($code, $genus); # Can have a nested transaction
     return $genus->species;
   };
 
@@ -438,6 +491,13 @@ C<next::method>.
     $class->next::method($attrs);
   }
 
+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>
@@ -502,8 +562,8 @@ instead:
                          },
   );
   
-  $translator->parser('DBIx::Class');
-  $translator->producer('DBIx::Class::File');
+  $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;
@@ -511,7 +571,7 @@ instead:
   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.
+namespace, which is currently left as an exercise for the reader.
 
 =head2 Schema versioning
 
@@ -626,8 +686,164 @@ The first sets the quotesymbols. If the quote i "symmetric" as " or '
   
   __PACKAGE__->storage->sql_maker->quote_char('"');
 
-is enough. If the left qoute differs form the right quote, the first 
+is enough. If the left quote differs form the right quote, the first 
 notation should be used. 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 to the superclass(es).
+
+=head3 Automatically creating related objects
+
+You might have a class C<Artist> which has many C<CD>s.  Further, you
+want to create a C<CD> object every time you insert an C<Artist> object.
+You can accomplish this by overriding C<insert>:
+
+  sub insert {
+    my ( $class, $args_ref ) = @_;
+    my $self = $class->next::method($args_ref);
+    $self->cds->new({})->fill_from_artist($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;
+
+  $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;
+  my $artist_rs = $schema->resultset('Artist');
+           # for example
+
+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.
+
 =cut