What is the most efficient way to filter documents with a similar structure to the one below based on the 'expanded_url' key's value. There are two more general questions here: * How do you filter documents based on a nested key(s)? * How do you filter documents based on the value of a key that resolves to an array of objects?

gistfile1.js

{
  "created_at":	"Tue, 01 Jan 2013 12:55:09 +0000",
	"entities":	{
		"hashtags":	[{
				"text":	"Clojure",
				"indices":	[39, 47]
			}],
		"urls":	[{
				"url":	"http://t.co/ythjuG5U",
				"expanded_url":	"http://benchmarksgame.alioth.debian.org/u32/benchmark.php?test=all&lang=clojure&lang2=java",
				"display_url":	"benchmarksgame.alioth.debian.org/u32/benchmark.…",
				"indices":	[118, 138]
			}],
		"user_mentions":	[]
	},
	"from_user":	"foo",
	"from_user_id":	000000000,
	"from_user_id_str":	"000000000",
	"from_user_name":	"Foo Bar",
	"geo":	null,
	"id":	0000000000000000000,
	"id_str":	"0000000000000000000",
	"iso_language_code":	"en",
	"metadata":	{
		"result_type":	"recent"
	},
	"profile_image_url":	"http://example.com/profile_images/000000000/avatar_normal.png",
	"profile_image_url_https":	"https://si0.twimg.com/profile_images/000000000/avatar_normal.png",
	"source":	"<a href="http://twitter.com/">web</a>",
	"text":	"New \"Programming Clojure\" still claims #Clojure is at \"The speed of hand-written Java code\" when it clearly isn't :-( http://t.co/ythjuG5U",
	"to_user":	null,
	"to_user_id":	0,
	"to_user_id_str":	"0",
	"to_user_name":	null
}

Discussion on this is here: rethinkdb/rethinkdb#211