how to get data from 3 collections in mongodb using node js?

Question

I have the below collections in mongodb

db.orders.find()

{ \"_id\" : ObjectId(\"5cc69ad493297eade15bacb7\"), \"item\" : \"card\         


        

Answer 1

You have to change data-type of mobile_no in users_nippon collection from string to NumberLong otherwise $lookup will not work. After correcting it, now you can use below aggregation query to get your desired result in the same format you want.

db.collection('users_nippon').aggregate([

        {
            $lookup: {
              from: "orders",
              localField: "mobile_no",
              foreignField: "user_mob",
              as: "orders_data"
            }
        },
        {
            $unwind: "$orders_data"
        },
        {
            $lookup: {
                from: "items",
                localField: "orders_data.item",
                foreignField: "item",
                as: "orders_data.items_data"
            }
        },
        {
            $unwind: "$orders_data.items_data"
        }
    ]).toArray(function(err, list) {
        if (err) throw err;
        console.log(JSON.stringify(list));
        res.send(JSON.stringify(list));
        });

this is the tested and working solution.