Question 117747 in Mongodb Question posted in
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Mongodb – mongoose divide two fields in put request

Can I update a field of a document with a division of two fields? Using Node and MongoDB, I’m trying to create a rating function, and I have to make a division, but nothing seems to work. I want the new value of rating to be, the current one divided by the number of votes.


router.put("/:id/:rating", async (req, res) => {
    const movie_rating = parseInt(req.params.rating);
    try {
        const updatedMovie = await Movie.findByIdAndUpdate(
            req.params.id,
            {
                $inc: { noVotes: 1 },
                $inc: { rating: movie_rating },
                $divide: { rating: [rating, noVotes] },
                // rating: { $divide: [rating, noVotes] }
            },
            { new: true }
        );
        res.status(200).json(updatedMovie);
    } catch (err) {
        res.status(500).json(err);
    }
});
Tags:

2

Answers


  1. 0

    You need to change few things

    Sample

    db.collection.update({},
[
  {
    "$set": {
      "key2": {
        $add: [
          "$key2",
          1
        ]
      },
      key3: {
        "$divide": [
          {
            $add: [
              "$key2",
              1
            ]
          },
          "$key"
        ]
      },
      
    }
  }
],
{
  "multi": true,
  "upsert": false
})
    1. You need aggregate update as you need divide
    2. You cannot use the updated value in the same operation
    3. You cannot combine $inc, $set in aggregate update
    4. Alternatively, you can use $add instead $inc
    5. you can reperform the operation for the divide operation than making another update call
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  2. 0

    This can be done with $set,
    It will look like this:

    router.put("/:id/:rating", async (req, res) => {
  const movie_rating = parseInt(req.params.rating);
  try {
    const updatedMovie = await Movie.findByIdAndUpdate(
      req.params.id,
      [
        {
          $set: {
            noVotes: { $sum: ["$noVotes", 1] },
            rating: { $sum: ["$rating", movie_rating] },
            averageRating: { $divide: ["$rating", "$noVotes"] },
          },
        },
      ],
      { new: true }
    );
    res.status(200).json(updatedMovie);
  } catch (err) {
    res.status(500).json(err);
  }
});
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