Unable to find source-code formatter for language: mongodb. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml db.test.drop() db.test.insert({ "_id" : 1, "aa" : [ "bb" : { "id" : "1611e293-61c4-4028-b6fd-c5909247b020" , "type" : "form_charger" } ] }) db.form_charger.insert({ "_id" : 1, "id" : "1611e293-61c4-4028-b6fd-c5909247b020" }) db.test.aggregate([{ '$lookup' : { from: 'form_charger' , localField: 'aa.0.bb.id' , foreignField: 'id' , as: 'data_bb' } }]) The result of * data_bb * always empty.