$dateFromString

The $dateFromString operator is used to convert a date/time string to a date object. This operation can be useful when dealing with string representations of dates that need to be manipulated or queried as date objects.

Syntax

{
    $dateFromString: {
        dateString: < string > ,
        format: < string > ,
        timezone: < string > ,
        onError: < expression > ,
        onNull: < expression >
    }
}

Parameters

Parameter Description
dateString The date/time string to convert to a date object.
format (Optional) The date format specification of the dateString.
timezone (Optional) The timezone to use to format the date.
onError (Optional) The value to return if an error occurs while parsing the dateString.
onNull (Optional) The value to return if the dateString is null or missing.

Examples

Consider this sample document from the stores collection.

{
    "_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
    "name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
    "location": {
        "lat": -89.2384,
        "lon": -46.4012
    },
    "staff": {
        "totalStaff": {
            "fullTime": 8,
            "partTime": 20
        }
    },
    "sales": {
        "totalSales": 75670,
        "salesByCategory": [
            {
                "categoryName": "Wine Accessories",
                "totalSales": 34440
            },
            {
                "categoryName": "Bitters",
                "totalSales": 39496
            },
            {
                "categoryName": "Rum",
                "totalSales": 1734
            }
        ]
    },
    "promotionEvents": [
        {
            "eventName": "Unbeatable Bargain Bash",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 6,
                    "Day": 23
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 7,
                    "Day": 2
                }
            },
            "discounts": [
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 7
                },
                {
                    "categoryName": "Bitters",
                    "discountPercentage": 15
                },
                {
                    "categoryName": "Brandy",
                    "discountPercentage": 8
                },
                {
                    "categoryName": "Sports Drinks",
                    "discountPercentage": 22
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 19
                }
            ]
        },
        {
            "eventName": "Steal of a Deal Days",
            "promotionalDates": {
                "startDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 21
                },
                "endDate": {
                    "Year": 2024,
                    "Month": 9,
                    "Day": 29
                }
            },
            "discounts": [
                {
                    "categoryName": "Organic Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "White Wine",
                    "discountPercentage": 20
                },
                {
                    "categoryName": "Sparkling Wine",
                    "discountPercentage": 19
                },
                {
                    "categoryName": "Whiskey",
                    "discountPercentage": 17
                },
                {
                    "categoryName": "Vodka",
                    "discountPercentage": 23
                }
            ]
        }
    ]
}

Example 1: Convert promotional event dates to ISO dates

This query constructs full ISO date strings from individual year, month, and day fields using $concat and converts them to startDate and endDate using $dateFromString. It’s useful when date components are stored separately in documents.

db.stores.aggregate([
  {
    $match: { _id: "e6410bb3-843d-4fa6-8c70-7472925f6d0a" }
  },
  {
    $unwind: "$promotionEvents"
  },
  {
    $project: {
      eventName: "$promotionEvents.eventName",
      startDate: {
        $dateFromString: {
          dateString: {
            $concat: [
              { $toString: "$promotionEvents.promotionalDates.startDate.Year" },
              "-",
              {
                $cond: {
                  if: { $lt: ["$promotionEvents.promotionalDates.startDate.Month", 10] },
                  then: { $concat: ["0", { $toString: "$promotionEvents.promotionalDates.startDate.Month" }] },
                  else: { $toString: "$promotionEvents.promotionalDates.startDate.Month" }
                }
              },
              "-",
              {
                $cond: {
                  if: { $lt: ["$promotionEvents.promotionalDates.startDate.Day", 10] },
                  then: { $concat: ["0", { $toString: "$promotionEvents.promotionalDates.startDate.Day" }] },
                  else: { $toString: "$promotionEvents.promotionalDates.startDate.Day" }
                }
              }
            ]
          }
        }
      },
      endDate: {
        $dateFromString: {
          dateString: {
            $concat: [
              { $toString: "$promotionEvents.promotionalDates.endDate.Year" },
              "-",
              {
                $cond: {
                  if: { $lt: ["$promotionEvents.promotionalDates.endDate.Month", 10] },
                  then: { $concat: ["0", { $toString: "$promotionEvents.promotionalDates.endDate.Month" }] },
                  else: { $toString: "$promotionEvents.promotionalDates.endDate.Month" }
                }
              },
              "-",
              {
                $cond: {
                  if: { $lt: ["$promotionEvents.promotionalDates.endDate.Day", 10] },
                  then: { $concat: ["0", { $toString: "$promotionEvents.promotionalDates.endDate.Day" }] },
                  else: { $toString: "$promotionEvents.promotionalDates.endDate.Day" }
                }
              }
            ]
          }
        }
      }
    }
  }
])

This query returns the following result.

[
  {
    "_id": "e6410bb3-843d-4fa6-8c70-7472925f6d0a",
    "eventName": "Massive Markdown Mania",
    "startDate": "2024-09-21T00:00:00.000Z",
    "endDate": "2024-09-29T00:00:00.000Z"
  }
]

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