Sort by value of multiply field a and field b in mongodb

Question

I have farm collection that has apy and liquidity. I want to get top 10 results by order of value of apy * liquidity I tried like this.

var data = models.farm.find().sort({ $expr: { $multiply: ["$apy", "$liquidity"] } }).limit(10)

But it doesn't work well.
How can I get expected result?

Answer 1

Try adding another field with the value from apy * liquidity like this

  var data = await models.farm.aggregate([
    {
      $addFields: {
        apy_times_liquidity : { $multiply: ['$apy', '$liquidity'] }
      }
    },
    {
      $sort: { apy_times_liquidity : -1 }
    },
    { $limit: 6 }
  ])
    .exec()
    .then(result => {
      return result;
    })
    .catch(err => {
      console.log(err);
    });

  res.send({ data: data });