Introspection

The Graph API supports introspection of objects, which enables you to see all of the connections an object has without knowing its type ahead of time. To get this information, add metadata=1 to the object URL, and the resulting JSON will include a metadata property that lists all the supported connections for the given object. For example, you can see all the connections for the Developer Garage event above by fetching https://graph.facebook.com/331218348435?metadata=1. That outputs:

{
   "name": "Facebook Developer Garage Austin - SXSW Edition",
   "metadata": {
      "connections": {
         "feed": "http://graph.facebook.com/331218348435/feed",
         "picture": "https://graph.facebook.com/331218348435/picture",
         "invited": "https://graph.facebook.com/331218348435/invited",
         "attending": "https://graph.facebook.com/331218348435/attending",
         "maybe": "https://graph.facebook.com/331218348435/maybe",
         "noreply": "https://graph.facebook.com/331218348435/noreply",
         "declined": "https://graph.facebook.com/331218348435/declined"
      }
   }
}

The introspection feature is a useful and extensible way to find all the things your users are connected to.