Same aggregates with two differents results-CodePudding

I'm new to mongo and tried to return the result of an aggregation.

joinById: (collection, id, $lookup, res) => {

    var $match = {"_id": ObjectId(id) };

    MongoClient.connect(url, function (err, db) {
        if (err) throw err;
        var dbo = db.db("myDB");
        dbo.collection(collection)
            .aggregate([{ $match }, { $lookup }])
            .toArray(function (err, result) {
                if (err) throw err;
                const jsonable = stringify(result);
                res.status(200).json(jsonable)
                db.close();
            });
    });

}

I did it work at this first step but I needed to change something, because I cant figure how to return the result to the calling function.

So I did this change:

joinById2: async (collection, id, $lookup) => {

    const $match = {"_id": ObjectId(id) };

    const client = await MongoClient.connect(url);
    const table = client.db("myDB");
    const collect = table.collection(collection);
    const aggregate = collect.aggregate([{ $match }, { $lookup }]);
    const result = aggregate.toArray()

    return stringify(result);

},

Now I can return the value but ... The aggregate dont give any results.

I prefere the second way to write it, and already changed other function that are working. So I'd like to know: Why cant I get the same result ? How can I fix this ?

CodePudding user response：

I just missed the Promise.

const result = await aggregate.toArray()

With an await it works !

CodePudding user response：

You need to await for Promises

async (collection, id, $lookup) => {
    const $match = {"_id": ObjectId(id) };
    const client = await MongoClient.connect(url);
    const table = await client.db("myDB");
    const collect = await table.collection(collection);
    const aggregate = await collect.aggregate([{ $match }, { $lookup }]);
    const result = await aggregate.toArray()
    return stringify(result);
}