Understanding the Facebook Graph API - PHP

As a Facebook developer, it is important that you understand the Facebook Graph. Facebook also call this the "social graph."

Say, for example, you want to retrieve the following data from a Facebook user's profile:

• User ID
  
• Name
  
• Gender
  
• Facebook URL link

Facebook uses JSON objects when presenting user profile data. A user's profile can be obtained via their Facebook graph's sub-domain. 

According to Facebook, every object in the social graph contains a unique ID. So all Facebook users have a unique ID assigned to them.

Another thing you need to know is that you can access a Facebook user's information via the graph URL; you just need to append the Facebook user's ID. For example:

https://graph.facebook.com/ID

where "ID" is the actual user ID. The data are presented as JSON objects. For example, if your user ID is 747166266, you can access it in the address bar as follows:

https://graph.facebook.com/747166266

See the screen shot below:

The required get_facebook_cookie_function

This is the start of the PHP script discussion. We're going to analyze the sample script provided by the Facebook API. The first step is to get the Facebook cookie. This is will be used by the succeeding scripts to check whether or not the user has logged in to your website using their Facebook account.

To do this in your PHP web application, paste the following code at the top of your PHP scripts (the very first line of code):

<?php
define('FACEBOOK_APP_ID', '***YOUR FACEBOOK APPLICATION ID HERE***');
define('FACEBOOK_SECRET', '***YOUR FACEBOOK SECRET APPS KEY HERE***');
function get_facebook_cookie($app_id, $application_secret) {
  $args = array();
  parse_str(trim($_COOKIE['fbs_' . $app_id], '"'), $args);
  ksort($args);
  $payload = '';
  foreach ($args as $key => $value) {
    if ($key != 'sig') {
      $payload .= $key . '=' . $value;
    }
  }
  if (md5($payload . $application_secret) != $args['sig']) {
    return null;
  }
  return $args;
}
$cookie = get_facebook_cookie(FACEBOOK_APP_ID, FACEBOOK_SECRET);
?>

You need a Facebook Application ID and secret apps key, to be placed under "Define."