MongoDB /节点查找/匹配

Question

Currently I have 3 Schemas:

UserFavorite (This schema is supposed to be used to store the favorites the user has decided)

var UserFavoriteSchema = new Schema({
    _id: {
        type: Schema.ObjectId,
        auto: true
    },
    favoriteId: {
        type: Schema.ObjectId,
        required: true
    },
    userId: {
        type: Schema.ObjectId,
        required: true
    }
});

module.exports = mongoose.model('UserFavorite', UserFavoriteSchema);

Favorites (This schema holds the available favorites in the system)

var FavoriteSchema = new Schema({
    _id: {
        type: Schema.ObjectId,
        auto: true
    },
    storeId: {
        type: String,
        auto: true
    },
    name: {
        type: String,
        required: true
    },
    ...
});

module.exports = mongoose.model('Favorite', FavoriteSchema);

User Schema

var UserSchema = new Schema({
    _id: {
        type: Schema.ObjectId,
        auto: true
    },
    name: {
        type: String,
        required: true
    },
    password: {
        type: String,
        required: true
    },
    ...
});
module.exports = mongoose.model('User', UserSchema);

---

Everytime an user favorites an item (from Favorite collection) I will store the ID on UserFavorite.

My problem: I'm trying to retrieve all favorite data from a given user (all infos from Favorite that are presented on UserFavorite).

Here's my code:

    UserFavorite.aggregate([
                {
                    $match: {
                        "userId": mongoose.Types.ObjectId(userId)
                    }
                },
                {
                    $lookup: {
                        "from": "favorites",
                        "localField": "favoriteId",
                        "foreignField": "_id",
                        "as": "favorites"
                    }
                }
            ]).exec(function (err, data) {
                if(err){
                    //ERROR
                }else{
//Everything's okay

}

});

My expected result:

I expect to have each User favorite inside of Favorites array. (the 'as' from Lookup), like the following:

[
    {
        "userId": "5bc74f4ac42a2719b8827404",
        "favorites": [
            {
                "_id": "5bc7d92f4235972ea805664e",
                "thumbnail": "string",
                "storeId": "string",
                "name": "string",
            },
            {
                "_id": "5bc7d9414235972ea805664f",
                "thumbnail": "no_image",
                "storeId": "1234",
                "name": "Fulério Store",
            }
        ]
    },
]

But what I get is:

[
    {
        "userId": "5bc74f4ac42a2719b8827404",
        "favoriteId": "5bc7d92f4235972ea805664e",
        "favorites": [
            {
                "_id": "5bc7d92f4235972ea805664e",
                "thumbnail": "string",
                "storeId": "string",
                "name": "string",
                "__v": 0
            }
        ]
    },
    {
        "userId": "5bc74f4ac42a2719b8827404",
        "favoriteId": "5bc7d9414235972ea805664f",
        "favorites": [
            {
                "_id": "5bc7d9414235972ea805664f",
                "thumbnail": "no_image",
                "storeId": "1234",
                "name": "Fulério Store",
                "__v": 0
            }
        ]
    }
]

It brings the informations of each favorite of "UserFavorite", instead of putting all favorites from a given user into an array.

How could I get it working?

Thank you in advance!

Answer 1

You'll need to use the $group operator, what you've got now is akin to

1. Find every UserFavorite for the user_id (there are 2 items returned)
2. For each of those items, lookup that favorite

Try adding this as the last stage of the aggregation

{
    $group: {
         _id: "$userId",
         favoriteArray: {$addToSet: "$favorites"}
    }
}

The $group stage will roll them all up based on the userId