Drupal 7 Module Development

Node Access
Domain Access keeps track of two separate realms, but sets all three grant operations
to TRUE for each node. So this table stores just the data necessary to rebuild the node
access table.
To ensure that your data is present during rebuild, your module should implement
hook_node_load(). This will ensure that the data required by your implementation
of hook_node_access_records() is available to you.
It is important to load this data in hook_node_load() rather than
inside hook_node_access_records() for the following reason. Other
modules may wish to act based on your data – particularly modules
that implement hook_node_access_records_alter(). While
hook_node_load() allows the $node object to be altered and extended,
hook_node_access_records() does not. So it is your module's
responsibility to ensure that the data used by your node access logic is
loaded onto the $node object properly.
Since the Role Access module can always access $node->uid to derive its data, we
won't worry about data storage for our module.
Modifying the behavior of other modules
Our choice of Role Access as a sample module was deliberate for two reasons: first,
we can ignore the data storage issue discussed above; second, the role system gives
us a good opportunity to look at how other modules may modify the behavior of
node access modules.
If you saved and installed the Role Access code to this point, you will see that it
works just fine, but with two potential issues.
• For most sites, anonymous users are not allowed to create content but they
are allowed to view content. Since Role Access restricts the View operation
to users with the same role, this would mean that anonymous users cannot
view any content.
• All custom roles are also tagged as authenticated users (role id 2). This means
that any content created by someone in an 'administrator' role would also be
tagged for authenticated users. This seems too permissive.
We could write some logic into the Role Access module to handle these use cases,
but it may also be the case that the default functionality is proper. So rather than
edit the module or create some special module settings and exception handling, in
Drupal 7 we can write a simple extension module that will modify the behavior of
the parent module.
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