Can't manipulate mongoose query result - promise undefined

Question

I'm new to mongoose and promises, so it will probably be something I am not getting clear, here's the thing:

I'm writing my app (MEAN) where I have some web services stacked in my controller to retrieve and get things. I'll make an example.

exports.allowanceCheck = (req, res) => {

  let payload = req.body.excelparam
  let day = getDate(payload[0].data_accesso,1)
  var dummyVar

   return AccessList.aggregate([
    {'$match' : {'id': day}},
    {'$unwind' : '$employees'},
    {
      $group: {
        _id: '$id',
        count: { $sum: 1 }
      }
    }
   ])
  .exec()
  .then((list) => {
    console.log(list) //not working
    res.json(list)
    dummyVar = list
  })
  .catch((err) => {
    res.status(500).send(err)
    
  })

}
console.log(list) //not working
console.log(dummyVar) //not working

The web service works just fine, the client gets his response JSON:

[
    {
        "_id": "200830",
        "count": 2
    }
]

The problem I am getting now is that, if I want to do something with this "list" JSON data, I get an error that I'm trying to manipulate {undefined} stuff. (e.g. everywhere you see //not working - and probably anywhere else) So I can only send the data back and I am not able to manipulate anything.

I tried saving the promise and accessing it, didn't work.

What am I doing wrong?

thank you! :)

Answer 1

You can try the following approach for better understanding of the promise

    exports.allowanceCheck = (req, res) => {

    let payload = req.body.excelparam
    let day = getDate(payload[0].data_accesso, 1)

    functionAllowanceCheck(day).then((listResponse) => {
        console.log(listResponse) //working
        res.json(listResponse)
    }).catch((listError) => {
        res.status(500).send(listError)
    })

}

const functionAllowanceCheck = (day) => {
    return new Promise((resolve, reject) => {
        AccessList.aggregate([
            { '$match': { 'id': day } },
            { '$unwind': '$employees' },
            {
                $group: {
                    _id: '$id',
                    count: { $sum: 1 }
                }
            }
        ]).exec((err, list) => {
            if (err) {
                reject(err)
            } else {
                resolve(list)
            }
        })
    })
  }