[{"_id":{"$oid":"56e9978732beb44a2f2ac6ae"},"domain":"example.co.uk","good":[{"crawled":true,"added":{"$date":"2016-03-16T17:27:17.461Z"},"link":"/url-1"},{"crawled":false,"added":{"$date":"2016-03-16T17:27:17.461Z"},"link":"url-2"}]}]

db.collection.update({"domain":"example.co.uk"},[{$set:{good:{$ifNull:["$good",[]]}}},{$set:{good:{$concatArrays:["$good",{$cond:[{$in:["/url-1","$good.link"]},[],[{"crawled":false,"link":"/url-1"}]]}]}}}],{upsert:true})