db={"workoutDetailSchema":[{"_id":{"$oid":"6359a12fb9450da3d8d8cdd2"},"REF_Users":[{"$oid":"6359a0f1b9450da3d8d8cdc7"},{"$oid":"6359a070f1e84209e0c78fc2"}],"name":"Once"}],"users":[{"_id":{"$oid":"6359a070f1e84209e0c78fc2"},"REF_UserType":{"$oid":"63596323b679475de490500a"},"fName":"Billy"},{"_id":{"$oid":"6359a0f1b9450da3d8d8cdc7"},"REF_UserType":{"$oid":"63596323b679475de4905007"},"fName":"Mike"}],"usertypes":[{"_id":{"$oid":"63596323b679475de4905007"},"value":100,"name":"INS"},{"_id":{"$oid":"63596323b679475de490500a"},"value":200,"name":"CLS"}]}

db.workoutDetailSchema.aggregate([{"$lookup":{"from":"users","localField":"REF_Users","foreignField":"_id","as":"peopleLookup"}},{"$lookup":{"from":"usertypes","localField":"peopleLookup.REF_UserType","foreignField":"_id","as":"userTypeLookup"}},{"$project":{"people":{"$map":{"input":"$peopleLookup","as":"tempPeople","in":{"$mergeObjects":["$$tempPeople",{"userType":{"$first":{"$filter":{"input":"$userTypeLookup","cond":{"$eq":["$$tempPeople.REF_UserType","$$this._id"]}}}}}]}}}}},{"$unset":"people.REF_UserType"}])