db={"UserReview":[{_id:1,username:"John",content:"I liked the product"}],"UserReply":[{username:"John",content:"I liked the product",userReviewId:1,status:"REJECTED"},{username:"John",content:"cool",userReviewId:1,status:"APPROVED"}]}

db.UserReview.aggregate([{"$lookup":{"from":"UserReply","let":{id:"$_id"},"pipeline":[{$match:{$and:[{$expr:{$eq:["$$id","$userReviewId"]}},{status:"APPROVED"}]}}],"as":"replies"}}])