db={"likes":[{likedId:"xxx",userId:"123"},{likedId:"aaa",userId:"123"}],"posts":[{postId:"xxx"},{postId:"zzz"},],"comments":[{commentId:"aaa"}]}

db.likes.aggregate([{"$lookup":{"from":"posts","localField":"likedId","foreignField":"postId","as":"postData"}},{$match:{postData:{$ne:[]}}}])