Rules Based Way to Limit Node Creation (Quota) per Role, User, and Content Type

This quick tutorial will let you limit the creation of a certain number of nodes for any user with a specific role. For every content type and/or role you want to limit, (Eg.: Contributors limited to 4 posts, Admins are limited to 10 posts), you will need to create a separate rule for each.

Assumptions:

1. Are a familiar with Drupal 7.x and Rules 7.x
2. You are familiar with PHP enough to read it.

Basics:

1. A Content Type that you want to apply a limit to. Eg: "News Post"
2. A Role that will be limited. Eg: "Contributor"
3. A User with appropriate permissions to create "News Post", and has the role of "Contributor".

Modules:

1. Rules (plus all dependancies)
2. Rules Forms Support ( http://drupal.org/project/rules_forms)

Setup Rules Forms:

1. Configure Rules Forms (Configuration -> Rules -> Form Events)
2. Check ON:
3. • Enable event activation messages on forms
   • Enable form element inspection tool
4. Navigate to the node add form for your content type. Eg.: /node/add/news-post
5. Click the link at the top of the form to enable the form events. Eg.: "Activate events for rules_forms_news_post"
6. Refresh the node add page after it loads back

Create the Limiting Rule:

1. Create a new Rule (Configuration -> Rules -> Add new rule)
2. Name: "Contributor News Post Limit"
3. React on event: "Rules Forms" -> "News Post node form is being built" -- where "News Post" is the name of the content type that you want limited, as mentioned in the above steps.
4. Conditions:
5. • "User has role(s)"<- and add the role(s) that you want limited. Eg.: "Contributor"
   • "Execute custom PHP code":
     
     // Configure your settings: Node limit/quota & Content Type
$nodelimit = 10;
$content_type = 'news_post';

// Check it we are just editing an existing node, and quit if so
if(arg(0) == 'node'&& arg(2) == 'edit'){
return FALSE;
}

// Load the active user account
global $user;

// Drupal has a security feature called the Database Abstraction Layer.
// You have to build DB queries with variables that are defined in an array.
// Define the query string, where ":gdcuid" etc. are placeholders
$query = 'SELECT * FROM node WHERE uid=:gdcuid AND type=:gdctype';

// Define each placeholder
$variables = array(':gdcuid' => $user->uid, ':gdctype' => $content_type);

// Query the Drupal database
$result = db_query($query, $variables);

// Count the number of rows returned from the Drupal database
// From: http://api.drupal.org/api/drupal/includes%21database%21database.inc/function/db_query/7
$nodecount = $result->rowCount();

// Set the flag as to whether this Rule is effective or not
if ( $nodecount >= $nodelimit) {
return TRUE; // You will be over the accepted quota
} else {
return FALSE; // Still got room. Allow the new node.
}

5. Actions:
6. • Show a message on the site: Warning: "You have reached your allotted limit of posts. Please delete old posts to make room, and try again".
   • Page Redirect: ** Redirect to wherever you need, if you need **

Done. Feedback/improvements welcome!