Wykonywanie złączeń w mongodb z trzema kolekcjami?

Ok, wygląda na to, że masz mnóstwo problemów. Spróbuję je podsumować.

Problem 1:podany przez Ciebie kod zbiorczy nie kompiluje się.

db.user_movies.aggregate(
{$match : {mobile_no : mobile_no}},
{$unwind: "$movies" },
{$lookup: {from: "movies",localField: "movies",foreignField: "movie_id",as: "bmarks"}},
{$unwind : "$bmarks"},
{$match : {"bmarks.active": 1}},
{$group : { _id : "$_id", movies : {$push : "$bmarks"}, movie_ids: {$push : "$bmarks.movie_id"}}},
{$lookup: {from: "movie_comments", localField: "",foreignField: "movie_id",as: "comments"}},
{$unwind : "$comments"},
{$sort: {time_posted: -1}},
{$group: {_id: '$_id', comments : {$push : "$comments"}}},

Poprawka:

db.user_movies.aggregate([
{$match : {mobile_no : mobile_no}},
{$unwind: "$movies" },
{$lookup: {from: "movies",localField: "movies",foreignField: "movie_id",as: "bmarks"}},
{$unwind : "$bmarks"},
{$match : {"bmarks.active": 1}},
{$group : { _id : "$_id", movies : {$push : "$bmarks"}, movie_ids: {$push : "$bmarks.movie_id"}}},
{$lookup: {from: "movie_comments", localField: "",foreignField: "movie_id",as: "comments"}},
{$unwind : "$comments"},
{$sort: {time_posted: -1}},
{$group: {_id: '$_id', comments : {$push : "$comments"}}}])

Teraz załóżmy, że używasz tych samych danych, które podałeś.

Problem 2 :{$match : {"bmarks.active": 1}} nie pasuje do żadnego wpisu.

Poprawka:{$match : {"bmarks.active": 0}}

Problem 3 :Nie zdefiniowano pola wyszukiwania {$lookup: {from: "movie_comments", localField: "",foreignField: "movie_id",as: "comments"}}

Napraw :{$lookup: {from: "movie_comments", localField: "movie_ids",foreignField: "movie_id",as: "comments"}}

Problem 4:Brak etapu rozwijania dla movie_ids do poprzedniego wyszukiwania

Poprawka:{$unwind : "$movie_ids"}

Problem 5 :Brak czasu zaksięgowania pola {$sort: {time_posted: -1}}

Poprawka:uwzględnij pole przed sortowaniem

Tak więc, aby zebrać wszystko razem, potrzebujesz agregacji, aby wyglądało jak coś poniżej, aby wyodrębnić komentarze do każdego filmu.

db.user_movies.aggregate([
{$match : {mobile_no : mobile_no}},
{$unwind: "$movies"},
{$lookup: {from: "movies",localField: "movies",foreignField: "movie_id",as: "bmarks"}},
{$unwind : "$bmarks"},
{$match : {"bmarks.active": 0}},
{$group : { _id : "$_id", movies : {$push : "$bmarks"}, movie_ids: {$push : "$bmarks.movie_id"}}},
{$unwind : "$movie_ids"},
{$lookup: {from: "movie_comments", localField: "movie_ids",foreignField: "movie_id",as: "comments"}},
{$unwind : "$comments"},
{$group: {_id: '$_id', comments : {$push : "$comments"}}}])

Przykładowe wyjście

{
    "_id": ObjectId("5834ecf7432d92675bde9d83"),
    "comments": [{
        "_id": ObjectId("583d96d7e35f6e9c53c9e894"),
        "movie_id": "dallas00",
        "comment": "what a great movie."
    }, {
        "_id": ObjectId("583d96d7e35f6e9c53c9e895"),
        "movie_id": "dallas00",
        "comment": "awesome movie."
    }]
}

Aktualizacja:

db.user_movies.aggregate([
{$match : {mobile_no : mobile_no}},
{$unwind: {path: "$movies", includeArrayIndex: "moviePosition"}},
{$sort :  {moviePosition:1}},
{$lookup: {from: "movies",localField: "movies",foreignField: "movie_id",as: "bmarks"}},
{$unwind :"$bmarks"},
{$group : {_id : "$_id", movies : {$push : {movie_name:"$bmarks.movie_name", movie_id:"$bmarks.movie_id"} }}},
{$unwind : "$movies"},
{$lookup: {from: "movie_comments", localField: "movies.movie_id",foreignField: "movie_id",as: "comments"}},
{$unwind : "$comments"},
{$group:  {_id: "$movies.movie_id", movie_name: {$first:"$movies.movie_name"}, comments : {$push : {comment:"$comments.comment", time_posted:"$comments.time_posted"}}}},
{$sort :  {time_posted:-1}},
{$project:{_id:0, movie_id:"$_id", movie_name:1, comments: "$comments.comment"}}
]).pretty();