Facebook comment ID issue

Question

I am using FBML's fb:comments plugin on a Facebook app (which, although it's described as "legacy" on the Facebook developer site, seems to be the only way to get proper Facebook comment integration on a Canvas app? Please let me know if I'm wrong, it seems navigating the open ocean is easier than navigating the Facebook documentation). I'm also using the JavaScript SDK to subscribe to the comment.create event so I can keep track of who is commenting on my pages. Easy enough, and this seems to work to an extent, but while I have the following code:

    FB.Event.subscribe('comment.create', function(response) {
        console.log(response);
    });

This returns a nice JSON object including the following nugget:

commentID: "10150576473610309"

Great! I have a comment ID. So now I go to the Facebook graph API to get a bit more information about this comment (I want the text, author, etc.), so I issue the following in PHP because, according to the Facebook docs, everything on Facebook has a unique ID, and just hitting up the Graph API with this ID will give you some sweet info.

file_get_contents('http://graph.facebook.com/10150576473610309');

Oh no! This returns false. This is strange. So I check the API for all the comments relating to a specific page, and this gives me a list of the comments...but the ID of the one I just added is different, now it's in the format:

"id": "10150576473610309_20003210"

What is this additional underscore and number?! Calling the graph API with this comment ID gives me the comment info! Where and how (and why?) did this new ID come about? (Of course I tried the Facebook dev forum but it seems asking my mouse the same question would have achieved similar results).

Answer 1

Edit 13/06/2014: Be careful, the username field is now deprecated (thanks @Cyril-n)

Thanks to Jonathan & Tarmo I developped a mixed approch :

FB.Event.subscribe('comment.create',
    function(response) {
        var commentQuery = FB.Data.query("SELECT text, fromid FROM comment WHERE post_fbid='"+response.commentID+"' AND object_id IN (SELECT comments_fbid FROM link_stat WHERE url='"+response.href+"')");
        var userQuery = FB.Data.query("SELECT name FROM user WHERE uid in (select fromid from {0})", commentQuery);

        FB.Data.waitOn([commentQuery, userQuery], function() {
            var commentRow = commentQuery.value[0];
            var userRow = userQuery.value[0];
            console.log(userRow.name+" (id: "+commentRow.fromid+") posted the comment: "+commentRow.text);
        });
    }
);

With this you get all the info needed on the last comment posted.

PS: there is a field named 'username' in the table comment ( http://developers.facebook.com/docs/reference/fql/comment/ ) but it doesn't really seem to work (it says username "Anonymous user" when it isn't anonymous... that's why I used the second query to get the user info)

Answer 2

This is now the preferred way to get the comments from a comment box:

http://developers.facebook.com/blog/post/490

Anyway, about your question. I've found that facebook adds an id whenever they launch a new platform. For example, the id of an object for FQL, graph api, and old REST API are all different. To see this in action look at a photo in an album. All those ids separated by an underscore are: The graph api id, the FQL aid, the photo graph api unique id, and some additional ids are possible, depending on who uploaded it. Those mysterious numbers that get added after your comments are just some kind of comment counter for your application, or a group of applications, basically useless.

So, from my experience mixing facebook platforms is always a bad idea, involving a lot of experimentation and hacks. If it's possible always use a singe platform, the graph api is the best bet right now.