Question 186869 in Javascript Question posted in
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Javascript – dateDiff mongoDb rounding off the difference

My aggregate query

'$dateDiff': 
    { 
        'startDate': '$updatedAt', 
        'endDate': new Date(), 
        'unit': "hour" 
    }

Example: My updatedAt is 10:00 (2023-06-08T10:00:00.502+00:00)
and my now is 1:50 (2023-06-08T13:54:00.502+00:00 )

My expected dateDiff is 3 but this is returning me 4.
Its rounding off but I want it to floor. How to achieve this ?

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2

Answers


  1. 0 
    db.collection.aggregate([
  {
    $project: {
      dateDiff: {
        // floor the result of division
        $floor: {
          // divide the difference of dates by 1000 * 60 * 60 to get the difference in hours
          $divide: [
            {
              // subtract the dates to get the difference in milliseconds
              $subtract: [new Date(), '$updatedAt'],
            },
            1000 * 60 * 60,
          ],
        },
      },
    },
  },
]);
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  2. 0

    Use below as template

    db.collection.aggregate([   {
    $match: {
      updatedAt: {
        $date: {
          $year: 2023,
          $month: 6,
          $day: 8,
          $hour: 10,
        },
      },
    },   },   {
    $dateDiff: {
      startDate: '$updatedAt',
      endDate: new Date(),
      unit: "hour",
    },   },   {
    $floor: {
      $dateDiff: {
        startDate: '$updatedAt',
        endDate: new Date(),
        unit: "hour",
      },
    },   }, ]);

    will return the number of hours between the updatedAt field and the current time. The $floor operator will then round down the result to the nearest integer.

    The reason why your original query was returning 4 is because the $dateDiff operator rounds up the result. This is because the $dateDiff operator uses the IEEE 754 double-precision floating-point format to represent numbers. This format has a limited number of digits after the decimal point, so rounding up is necessary to ensure that the result is accurate.

    The $floor operator, on the other hand, does not round up. It simply rounds down the result to the nearest integer. This is why the $floor operator will return 3 in this case.
    $dateDiff pipeline stage is not supported in MongoDB 4.0. It was introduced in MongoDB 4.2.

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