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=10ea02359c56fbf6dc93618fa88be5daf2a7dd13;hpb=181a28f4e04c13a37fe4a5b6357d85e1da63dbc4;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Manual/Cookbook.pod b/lib/DBIx/Class/Manual/Cookbook.pod
index 10ea023..52bb889 100644
--- a/lib/DBIx/Class/Manual/Cookbook.pod
+++ b/lib/DBIx/Class/Manual/Cookbook.pod
@@ -12,7 +12,7 @@ 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
@@ -24,7 +24,7 @@ paged resultset, which will fetch only a small number of records at a time:
 The C<page> attribute does not have to be specified in your search:
 
   my $rs = $schema->resultset('Artist')->search(
-    {},
+    undef,
     {
       rows => 10,
     }
@@ -72,19 +72,24 @@ 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:
+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,
     {
-      cols => [qw/ name /]
+      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
@@ -102,18 +107,21 @@ to access the returned value:
   );
 
   # Equivalent SQL:
-  # SELECT name name, LENGTH( name ) name_length
+  # SELECT name name, LENGTH( name )
   # 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:
+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
-can get the value using the C<get_column> accessor:
+have to fetch the value using the C<get_column> accessor:
 
   my $name_length = $artist->get_column('name_length');
 
@@ -134,10 +142,12 @@ any of your aliases using either of these:
       select => [
         { distinct => [ $source->columns ] }
       ],
-      as => [ $source->columns ]
+      as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
     }
   );
 
+  my $count = $rs->next->get_column('count');
+
 =head3 SELECT COUNT(DISTINCT colname)
 
   my $rs = $schema->resultset('Foo')->search(
@@ -169,6 +179,61 @@ L<DBIx::Class> supports C<GROUP BY> as follows:
   # 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
 
 You can use the C<join> attribute to allow searching on, or sorting your
@@ -260,9 +325,8 @@ 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.
+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
@@ -349,6 +413,84 @@ 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
@@ -357,24 +499,22 @@ example of the recommended way to use it:
 
   my $genus = $schema->resultset('Genus')->find(12);
 
+  my $coderef2 = sub {
+    $genus->extinct(1);
+    $genus->update;
+  };
+
   my $coderef1 = sub {
-    my ($schema, $genus, $code) = @_;
     $genus->add_to_species({ name => 'troglodyte' });
     $genus->wings(2);
     $genus->update;
-    $schema->txn_do($code, $genus); # Can have a nested transation
+    $schema->txn_do($coderef2); # Can have a nested transaction
     return $genus->species;
   };
 
-  my $coderef2 = sub {
-    my ($genus) = @_;
-    $genus->extinct(1);
-    $genus->update;
-  };
-
   my $rs;
   eval {
-    $rs = $schema->txn_do($coderef1, $schema, $genus, $coderef2);
+    $rs = $schema->txn_do($coderef1);
   };
 
   if ($@) {                             # Transaction failed
@@ -393,7 +533,7 @@ in the future.
 
 =head2 Many-to-many relationships
 
-This is straightforward using L<DBIx::Class::Relationship::ManyToMany>:
+This is straightforward using L<ManyToMany|DBIx::Class::Relationship/many_to_many>:
 
   package My::DB;
   # ... set up connection ...
@@ -431,19 +571,61 @@ It's as simple as overriding the C<new> method.  Note the use of
 C<next::method>.
 
   sub new {
-    my ( $class, $attrs ) = @_;
+    my ( $self, $attrs ) = @_;
 
     $attrs->{foo} = 'bar' unless defined $attrs->{foo};
 
-    $class->next::method($attrs);
+    $self->next::method($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.  Replace C<foo> with the column/method of your choice.
+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)
 
-  use overload '""' => 'foo', fallback => 1;
+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
 
@@ -469,7 +651,9 @@ To create a DBIx::Class schema from an existing database:
 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
+  sqlt --from SQL::Translator::Parser::DBIx::Class 
+       --to MySQL 
+       --DBIx::Class "MySchema.pm" > Schema1.sql
   
 And import using the mysql client:
 
@@ -496,14 +680,14 @@ instead:
       validate             => $validate       ||  0,
       parser_args          => {
          'DBIx::Schema'    => $schema,
-                              }
+                              },
       producer_args   => {
           'prefix'         => 'My::Schema',
-                         }
+                         },
   );
   
-  $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 +695,7 @@ 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
 
@@ -552,14 +736,14 @@ described under C<Schema import/export>.
 Use C<sqlt> to transform your schema into an SQL script suitable for your
 customer's database. E.g. for MySQL:
 
-  sqlt --from DBIx::Class
+  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 DBIx::Class
+  sqlt --from SQL::Translator::DBIx::Class
        --to PostgreSQL
        --DBIx::Class "MySchema.pm" > Schema1.pgsql.sql
 
@@ -587,7 +771,7 @@ 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 DBIx::Class
+  sqlt --from SQL::Translator::DBIx::Class
        --to MySQL
        --DBIx::Class "Anything.pm" > Schema2.mysql.sql
 
@@ -602,32 +786,412 @@ 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 (Se more names
-in SQL::Abstract::Limit -documentation.
+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
+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 quotes for the generated SQL. 
+=head2 Setting quoting for the generated SQL. 
 
-If the database contains columnames with spaces and/or reserved words, the
-SQL-query needs to be quoted. This is done using:
+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 quotesymbols. If the quote i "symmetric" as " or '
+The first sets the quote characters. Either a pair of matching
+brackets, or a C<"> or C<'>:
   
   __PACKAGE__->storage->sql_maker->quote_char('"');
 
-is enough. If the left qoute 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. 
+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