X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FManual%2FIntro.pod;h=cd8b0917a461106299c956835a3d2ca3603a165e;hb=b03f30a3a6e04ff27de81710085f9f0aa95b11f0;hp=4625d06da5d3af17fa0ca53451291b12b40b6750;hpb=d88ecca6486a2b1c4b6e2f0440165b186aab39bc;p=dbsrgits%2FDBIx-Class-Historic.git

diff --git a/lib/DBIx/Class/Manual/Intro.pod b/lib/DBIx/Class/Manual/Intro.pod
index 4625d06..cd8b091 100644
--- a/lib/DBIx/Class/Manual/Intro.pod
+++ b/lib/DBIx/Class/Manual/Intro.pod
@@ -114,6 +114,10 @@ automatic row ordering:
   __PACKAGE__->load_components(qw/ Ordered /);
   __PACKAGE__->position_column('rank');
 
+Ordered will refer to a field called 'position' unless otherwise directed.  Here you are defining
+the ordering field to be named 'rank'.  (NOTE: Insert errors may occur if you use the Ordered 
+component, but have not defined a position column or have a 'position' field in your row.)
+
 Set the table for your class:
 
   __PACKAGE__->table('album');
@@ -225,7 +229,7 @@ second database you want to access:
 Note that L<DBIx::Class::Schema> does not cache connections for you. If you use
 multiple connections, you need to do this manually.
 
-To execute some sql statements on every connect you can add them as an option in
+To execute some SQL statements on every connect you can add them as an option in
 a special fifth argument to connect:
 
   my $another_schema = My::Schema->connect(
@@ -236,7 +240,7 @@ a special fifth argument to connect:
       { on_connect_do => \@on_connect_sql_statments }
   );
 
-See L<DBIx::Class::Schema::Storage::DBI/connect_info> for more information about
+See L<DBIx::Class::Storage::DBI/connect_info> for more information about
 this and other special C<connect>-time options.
 
 =head3 Via a database handle
@@ -397,6 +401,53 @@ L<DBIx::Class::ResultSet/ATTRIBUTES>.
 
 =head1 NOTES
 
+=head2 The Significance and Importance of Primary Keys
+
+The concept of a L<primary key|DBIx::Class::ResultSource/set_primary_key> in
+DBIx::Class warrants special discussion. The formal definition (which somewhat
+resembles that of a classic RDBMS) is I<a unique constraint that is least
+likely to change after initial row creation>. However this is where the
+similarity ends. Any time you call a CRUD operation on a row (e.g.
+L<delete|DBIx::Class::Row/delete>,
+L<update|DBIx::Class::Row/update>,
+L<discard_changes|DBIx::Class::Row/discard_changes>,
+etc.) DBIx::Class will use the values of of the
+L<primary key|DBIx::Class::ResultSource/set_primary_key> columns to populate
+the C<WHERE> clause necessary to accomplish the operation. This is why it is
+important to declare a L<primary key|DBIx::Class::ResultSource/set_primary_key>
+on all your result sources B<even if the underlying RDBMS does not have one>.
+In a pinch one can always declare each row identifiable by all its columns:
+
+ __PACKAGE__->set_primary_keys (__PACKAGE__->columns);
+
+Note that DBIx::Class is smart enough to store a copy of the PK values before
+any row-object changes take place, so even if you change the values of PK
+columns the C<WHERE> clause will remain correct.
+
+If you elect not to declare a C<primary key>, DBIx::Class will behave correctly
+by throwing exceptions on any row operation that relies on unique identifiable
+rows. If you inherited datasets with multiple identical rows in them, you can
+still operate with such sets provided you only utilize
+L<DBIx::Class::ResultSet> CRUD methods:
+L<search|DBIx::Class::ResultSet/search>,
+L<update|DBIx::Class::ResultSet/update>,
+L<delete|DBIx::Class::ResultSet/delete>
+
+For example, the following would not work (assuming C<People> does not have
+a declared PK):
+
+ my $row = $schema->resultset('People')
+                   ->search({ last_name => 'Dantes' })
+                    ->next;
+ $row->update({ children => 2 }); # <-- exception thrown because $row isn't
+                                  # necessarily unique
+
+So instead the following should be done:
+
+ $schema->resultset('People')
+         ->search({ last_name => 'Dantes' })
+          ->update({ children => 2 }); # <-- update's ALL Dantes to have children of 2
+
 =head2 Problems on RHEL5/CentOS5
 
 There used to be an issue with the system perl on Red Hat Enterprise