Creating Component Dependencies - MySQL

Now that we have created an association between our Comments component and the previously created News component, a potential problem presents itself. What happens if a user deletes a News entry which contains one or more Comment entries (attached)?

Nennius offers a simple solution for this scenario as well. Simply update the following data found in the DB Field array in the News component file ('/components/news.php'):

# define primary key attribute for news table

$f_db_info_array['id'] = (

        array (

               'db_field_name'        => 'id',

               'db_field_type'        => 'int',

               'db_field_length'      => 3,

               'db_primary_key'       => TRUE,

               # field is hidden from visibility at all times

               'hidden_all'           => TRUE

        )

        # setup dependency information to clean all associated comments as well upon deletion

        'db_dependency_tables'         => array(

                                              array ( 'db_table_name'        => 'comments',

                                                     'db_field_name'        => 'news_id',

                                                      'db_display_name'      => 'Comment' )

                                              ),

        'db_dependency_flush'          => TRUE

);

As you can see we've added two array keys to the 'id' descriptor array: 'db_dependency_tables' and 'db_depencency_flush'. The first, 'db_dependency_tables', contains an array of arrays - each array specifying information about a unique record dependency. Since only one dependency exists in our example application, only one array has been specified.

The second variable, 'db_depencency_flush', contains a boolean value that tells Nennius how to act in the event that a News record (with one or more Comments records attached) is deleted. In our case we specified 'TRUE', which means that all associated Comments will also be deleted. (Note: If we had specified 'FALSE' then Nennius would have refused to delete any News releases with one or more User Comments attached.)