Return data from mongoDB query in nodejs

Question

I am just started learning MEAN stack and I am stuck. I need to send the below query data to frontend.

router.get('/average', (req, res) => {
  Employees.aggregate([
    { $match: { "position": "sen" } },
    {
      $group: {
        _id: null,
        average: {
          $avg: "$salary"
        }
      }
    }
  ]);
});

I have tried doing this but it didn't work

router.get('/average', (req, res) => {
  Employees.find(function (err, docs) {
    res.json(docs);
  }).aggregate([
    { $match: { "position": "sen" } },
    {
      $group: {
        _id: null,
        average: {
          $avg: "$salary"
        }
      }
    }
  ]);
});

what lib are you using for mongodb? is it mongoose?

Aritra Chakraborty
– Aritra Chakraborty

2019-12-15 08:01:24 +00:00
Commented Dec 15, 2019 at 8:01 — Aritra Chakraborty
– Aritra Chakraborty, Commented Dec 15, 2019 at 8:01
yes I am using mongoose

user12187201
– user12187201

2019-12-15 08:05:14 +00:00
Commented Dec 15, 2019 at 8:05 — user12187201
– user12187201, Commented Dec 15, 2019 at 8:05

Aritra Chakraborty · Accepted Answer · 2019-12-15 08:08:14Z

1

In the first example you are not send the data to response, and in the second case the syntax is slightly messed up.

So mongoose returns a Promise and/or aggregate value as response, so below code should work just fine:

router.get('/average', (req, res) => {
  Employees.aggregate([
    { $match: { position: 'sen' } },
    {
      $group: {
        _id: null,
        average: {
          $avg: '$salary'
        }
      }
    }
  ])
  .then((result)=>{
    res.json(result)
  })
});

Also check out the documentation for mongoose: https://mongoosejs.com/docs/api/model.html#model_Model.aggregate

answered Dec 15, 2019 at 8:08

Aritra Chakraborty

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