Drupal 7 Module Development

Chapter 9
Rebuilding the {node_access} table
One of the trickier parts of the node access system is rebuilding the {node_access}
table. When you first install a node access module, you will notice a warning at the
top of the configuration page, prompting you to rebuild permissions.
As a site administrator, you should always rebuild permissions when prompted
to do so. As a module developer, you are responsible for ensuring that those
permissions are rebuilt correctly.
In our example module code, we avoided this issue by relying on data that is
always present in the $node object, the user's identity, from which we can derive the
user's roles. However, if your module relies on data not stored by Drupal core or
contributed modules – both of which should be listed as dependencies[] in your
module.info file – then it is your responsibility to store the data necessary to rebuild
the {node_access} table properly.
For example, let's look quickly at the Domain Access module. This module stores
information about its grants in the {domain_access} table, which mirrors much
of the data in {node_access}. The table schema is as follows:
$schema['domain_access'] = array(
'fields' => array(
'nid' => array('type' => 'int', 'unsigned' => TRUE, 'not null'
=> TRUE, 'default' => 0),
'gid' => array('type' => 'int', 'unsigned' => TRUE, 'not null'
=> TRUE, 'default' => 0),
'realm' => array('type' => 'varchar', 'length' => '255', 'not
null' => TRUE, 'default' => '')),
'primary key' => array('nid', 'gid', 'realm'),
'indexes' => array(
'nid' => array('nid')),
);
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