NAME

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

VERSION

version 2.007004

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.

cpanm DBIx::Class::Helpers

perl -MCPAN -e shell
install DBIx::Class::Helpers