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=7e9a810969b89da1a423b76f20f3b802767b51a0;hpb=83ab85eaf574f3ffe429f74d595095162cf1cdaa;p=dbsrgits%2FDBIx-Class.git

diff --git a/lib/DBIx/Class/Manual/Cookbook.pod b/lib/DBIx/Class/Manual/Cookbook.pod
index 7e9a810..52bb889 100644
--- a/lib/DBIx/Class/Manual/Cookbook.pod
+++ b/lib/DBIx/Class/Manual/Cookbook.pod
@@ -72,8 +72,10 @@ 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,
@@ -85,6 +87,9 @@ specify which ones you need:
   # 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
@@ -94,7 +99,7 @@ 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(
-    undef,
+    {},
     {
       select => [ 'name', { LENGTH => 'name' } ],
       as     => [qw/ name name_length /],
@@ -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');
 
@@ -129,12 +137,12 @@ any of your aliases using either of these:
 =head3 SELECT DISTINCT with multiple columns
 
   my $rs = $schema->resultset('Foo')->search(
-    undef,
+    {},
     {
       select => [
         { distinct => [ $source->columns ] }
       ],
-      as => [ $source->columns ]
+      as => [ $source->columns ] # remember 'as' is not the same as SQL AS :-)
     }
   );
 
@@ -143,7 +151,7 @@ any of your aliases using either of these:
 =head3 SELECT COUNT(DISTINCT colname)
 
   my $rs = $schema->resultset('Foo')->search(
-    undef,
+    {},
     {
       select => [
         { count => { distinct => 'colname' } }
@@ -157,7 +165,7 @@ any of your aliases using either of these:
 L<DBIx::Class> supports C<GROUP BY> as follows:
 
   my $rs = $schema->resultset('Artist')->search(
-    undef,
+    {},
     {
       join     => [qw/ cds /],
       select   => [ 'name', { count => 'cds.cdid' } ],
@@ -171,9 +179,13 @@ 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 DBIx::Class::ResultSet class by inheriting from it
+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;
@@ -382,7 +394,7 @@ 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(
-    undef,
+    {},
     {
       prefetch => {
         cd => 'artist'
@@ -401,6 +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
@@ -443,7 +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 ...
@@ -481,11 +571,13 @@ 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> 
@@ -498,9 +590,42 @@ 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
 
@@ -526,7 +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:
 
@@ -609,14 +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
 
@@ -644,7 +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
 
@@ -659,33 +786,35 @@ 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 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. 
+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
 
@@ -710,11 +839,11 @@ You can accomplish this by overriding C<store_column>:
   }
 
 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).
+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, you
+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:
 
@@ -760,7 +889,7 @@ dumping it. For example,
 
   use Data::Dumper;
 
-  $Data::Dumper::Freezer = '_dumper_hook';
+  local $Data::Dumper::Freezer = '_dumper_hook';
 
   my $cd = $schema->resultset('CD')->find(1);
   print Dumper($cd);
@@ -774,11 +903,11 @@ 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,
+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
+  # 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.
@@ -856,4 +985,213 @@ If you are using PK::Auto, this is straightforward:
 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