$objectToArray

The $objectToArray operator is used to transform a document (object) into an array of key-value pairs. Each key-value pair in the resulting array is represented as a document with k and v fields. This operator is useful when you need to manipulate or analyze the structure of documents within your collections.

Syntax

{ $objectToArray: <object> }

Parameters

Parameter Description
<object> The document (object) to be transformed into an array of key-value pairs.

Examples

Given a sample JSON document representing a store, we can use the $objectToArray operator to transform various parts of this document.

Example 1: Transforming the location object

The example aggregation pipeline transforms the location object into an array of key-value pairs.

db.stores.aggregate([
  {
    $project: {
      locationArray: { $objectToArray: "$location" }
    }
  },
  {
    $limit: 2  // Limit output to first 5 documents
  }
])

The output represents the result of using the $objectToArray aggregation operator on the location field for each document.

  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "locationArray": [
      {
        "k": "lat",
        "v": -74.0427
      },
      {
        "k": "lon",
        "v": 160.8154
      }
    ]
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "locationArray": [
      {
        "k": "lat",
        "v": 61.3945
      },
      {
        "k": "lon",
        "v": -3.6196
      }
    ]
  }

Example 2: Transforming the salesByCategory array

If you want to transform the salesByCategory array, you would first need to unwind the array and then apply the $objectToArray operator.

db.stores.aggregate([
  { $unwind: "$sales.salesByCategory" },
  {
    $project: {
      salesByCategoryArray: { $objectToArray: "$sales.salesByCategory" }
    }
  },
  { 
    $limit: 2
  }
])

Converting subdocuments to key-value pairs is often used when you want to dynamically process field names, especially when: - Building generic pipelines. - Mapping field names into key-value structures for flexible transformations or further processing.

[
  {
    "_id": "a715ab0f-4c6e-4e9d-a812-f2fab11ce0b6",
    "salesByCategoryArray": [
      {
        "k": "categoryName",
        "v": "Stockings"
      },
      {
        "k": "totalSales",
        "v": 25731
      }
    ]
  },
  {
    "_id": "923d2228-6a28-4856-ac9d-77c39eaf1800",
    "salesByCategoryArray": [
      {
        "k": "categoryName",
        "v": "Lamps"
      },
      {
        "k": "totalSales",
        "v": 19880
      }
    ]
  }
]

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