DBIx::Class::Helper::Row::OnColumnChange(3pm)		User Contributed Perl Documentation	     DBIx::Class::Helper::Row::OnColumnChange(3pm)

NAME

       DBIx::Class::Helper::Row::OnColumnChange - Do things when the values of a column change

VERSION

       version 2.013002

SYNOPSIS

	package MyApp::Schema::Result::Account;

	use parent 'DBIx::Class::Core';

	__PACKAGE__->load_components(qw(Helper::Row::OnColumnChange));

	__PACKAGE__->table('Account');

	__PACKAGE__->add_columns(
	   id => {
	      data_type 	=> 'integer',
	      is_auto_increment => 1,
	   },
	   amount => {
	      data_type 	 => 'float',
	      keep_storage_value => 1,
	   },
	);

	__PACKAGE__->before_column_change(
	  amount => {
	     method   => 'bank_transfer',
	     txn_wrap => 1,
	  }
	);

	sub bank_transfer {
	  my ($self, $old_value, $new_value) = @_;

	  my $delta = abs($old_value - $new_value);
	  if ($old_value < $new_value) {
	     Bank->subtract($delta)
	  } else {
	     Bank->add($delta)
	  }
	}

	1;

       or with DBIx::Class::Candy:

	package MyApp::Schema::Result::Account;

	use DBIx::Class::Candy -components => ['Helper::Row::OnColumnChange'];

	table 'Account';

	column id => {
	   data_type	     => 'integer',
	   is_auto_increment => 1,
	};

	column amount => {
	   data_type	      => 'float',
	   keep_storage_value => 1,
	};

	before_column_change amount => {
	   method   => 'bank_transfer',
	   txn_wrap => 1,
	};

	sub bank_transfer {
	  my ($self, $old_value, $new_value) = @_;

	  my $delta = abs($old_value - $new_value);
	  if ($old_value < $new_value) {
	     Bank->subtract($delta)
	  } else {
	     Bank->add($delta)
	  }
	}

	1;

DESCRIPTION

       This module codifies a pattern that I've used in a number of projects, namely that of doing something when a column changes it's value in
       the database.  It leverages DBIx::Class::Helper::Row::StorageValues for passing in the $old_value, which do not have to use.  If you leave
       the "keep_storage_value" out of the column definition it will just pass "undef" in as the $old_value.  Also note the "txn_wrap" option.
       This allows you to specify that you want the call to "update" and the call to the method you requested to be wrapped in a transaction.  If
       you end up calling more than one method due to multple column change methods and more than one specify "txn_wrap" it will still only wrap
       once.

       I've gone to great lengths to ensure that order is preserved, so "before" and "around" changes are called in order of definition and
       "after" changes are called in reverse order.

       To be clear, the change methods only get called if the value will be changed after "update" runs.  It correctly looks at the current value
       of the column as well as the arguments passed to "update".

METHODS

   before_column_change
	__PACKAGE__->before_column_change(
	  col_name => {
	     method   => 'method', # <-- anything that can be called as a method
	     txn_wrap => 1,	   # <-- true if you want it to be wrapped in a txn
	  }
	);

       Note: the arguments passed to "method" will be "$self, $old_value, $new_value".

   after_column_change
	__PACKAGE__->after_column_change(
	  col_name => {
	     method   => 'method', # <-- anything that can be called as a method
	     txn_wrap => 1,	   # <-- true if you want it to be wrapped in a txn
	  }
	);

       Note: the arguments passed to "method" will be "$self, $old_value, $new_value".

   around_column_change
	__PACKAGE__->around_column_change(
	  col_name => {
	     method   => 'method', # <-- anything that can be called as a method
	     txn_wrap => 1,	   # <-- true if you want it to be wrapped in a txn
	  }
	);

       Note: the arguments passed to "method" will be "$self, $next, $old_value, $new_value".

       Around is subtly different than the other two callbacks.  You must call $next in your method or it will not work at all.  A silly example
       of how this is done could be:

	sub around_change_name {
	  my ($self, $next, $old, $new) = @_;

	  my $govt_records = $self->govt_records;

	  $next->();

	  $govt_records->update({ name => $new });
	}

       Note: the above code implies a weird database schema.  I haven't actually seen a time when I've needed around yet, but it seems like there
       is a use-case.

       Also Note: you don't get to change the args to $next.  If you think you should be able to, you probably don't understand what this
       component is for.  That or you know something I don't (equally likely.)

CANDY EXPORTS

       If used in conjunction with DBIx::Class::Candy this component will export:

       before_column_change
       around_column_change
       after_column_change

AUTHOR

       Arthur Axel "fREW" Schmidt <frioux+cpan@gmail.com>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2012 by Arthur Axel "fREW" Schmidt.

       This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

perl v5.14.2							    2012-06-18			     DBIx::Class::Helper::Row::OnColumnChange(3pm)