Non-trivial Facebook FQL example

This post will demonstrate a few non-trivial FQL calls from Javascript, including batching interdependent queries in one request. The example queries all participants of a public Facebook event and gets their names and any public status updates they’ve posted recently. It then goes on to find all friend-relations between the event participants and graphs those with an InfoVis Hypertree. I haven’t spent time on browser-compatibility in result-rendering (sorry!), but the actual queries work fine across browsers. You can try out the example here. The network-graph more-or-less only works in Google Chrome.

The demo was created for a session I did with Filip Wahlberg at the New Media Days conference. The session was called “Hack it, Mash it” and involved us showing off some of the stuff we do at and then demonstrating what sort of info can be pulled from Facebook. Amanda Cox was on the next morning and pretty much obliterated us with all the great interactive visualizations the New York Times builds, but that was all right.

Anyway, on to the code. Here are the three queries

var eventquery = FB.Data.query(
	'select uid from event_member ' +
	'where rsvp_status in ("attending", "unsure") ' +
		'and eid = 113151515408991 '

var userquery = FB.Data.query(
'select uid, name from user ' +
'where uid in  ' +
	' (select uid from {0})', eventquery

var streamquery = FB.Data.query(
	'select source_id, message from stream ' +
	'where ' +
	'updated_time > "2010-11-04" and ' +
	'source_id in ' +
		'(select uid from {0}) ' +
	'limit 1000 '
	, eventquery

FB.Data.waitOn([eventquery, userquery, streamquery],
	function () {
		// do something interesting with the data

Once the function passed to waitOn executes, all the queries have executed and results are available. The neat thing is that FB.Data bundles the queries so that, even though the last two queries depend on the result of the first one to execute, the browser only does one request. Facebook limits the number of results returned from queries on the stream table (which stores status updates and similar). Passing a clause on ‘updated_time’ seems to arbitrarily increase this number.

So now that we have the uid’s of all the attendees, how do we get the friend-relations between those Facebook users? Generally, Facebook won’t give you the friends of a random user without your app first getting permission from said user. Facebook will tell you whether any two users are friends and this is done by querying the friend table. So I wrote this little query which handily gets all the relations in a set of uids. Assume you’ve stored all the uids in an array:

var uidstring = uids.join(",");
var friendquery = FB.Data.query(
	'select uid1, uid2 ' +
	'from friend ' +
	'where uid1 in ({0}) and uid2 in ({0})'
	, uidstring

FB.Data.waitOn([friendquery], function () {
	// do something with the relations, like draw a graph

Neat huh? The full script can be found here:

Transatlantic Facebook application performance woes

Someone I follow on Twitter reported having problems getting a Facebook application to perform. I don’t know what they are doing so this post is just guessing at their problem, but the fact is that — if you’re not paying attention — you can easily shoot yourself in the foot when building and deploying Facebook apps. The diagram below depicts a random fbml Facebook app deployed to a server located in Denmark being used by a user also situated in Denmark. Note that Facebook doesn’t yet have a datacenter in Europe (they have one on each coast in the US).


The following exchange takes place:

  1. User requests some page related to the application from Facebook
  2. Facebook realizes that serving this request requires querying the application and sends a request for fbml to the app
  3. The app gets the request and decides that in order to respond, it has to query the Facebook API for further info
  4. The Facebook API responds to the query
  5. The application uses the query results and the original request to create a fbml response that is sent to Facebook
  6. Facebook gets the fbml, validates it and macroexpand various fbml tags
  7. Facebook sends the complete page to the user

… so that adds up 6 transatlantic requests pr. page requested by the user. Assuming a 250ms ping time from the Danish app-server to the Facebook datacenter this is a whopping 1.5s latency on top of whatever processing time your server needs AND the time taken by Facebook to process your API request and validate your fbml.

So what do you do? Usually steps 3 and 4 can be eliminated through careful use of fbml and taking advantage of the fact that Facebook includes the ids of all the requesting users friends. Going for an iframe app is also helpful because it eliminates one transatlantic roundtrip and spares Facebook from having to validate any fbml. A very effective measure if you insist on fbml, is simply getting a server stateside — preferably someplace with low ping times to Facebook datacenters. There are plenty of cheap hosting options around, Joyent will even do it for free (I’m not affiliated in any way).