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$objectToArray（表达式操作符）

定义

$objectToArray

将文档转换为数组。返回数组包含原始文档中每个字段/值对的一个元素。返回数组中的每个元素都是一份包含两个字段 k 和 v 的文档：

k 字段包含原始文档中的字段名称。
v 字段包含原始文档中该字段的值。

$objectToArray 通过以下语法实现：

{ $objectToArray: <object> }

The <object> expression can be any valid expression as long as it resolves to a document object. $objectToArray applies to the top-level fields of its argument. If the argument is a document that itself contains embedded document fields, the $objectToArray does not recursively apply to the embedded document fields.

有关表达式的更多信息，请参阅表达式。

行为

有关表达式的更多信息，请参阅表达式。

例子

结果

{ $objectToArray: { item: "foo", qty: 25 } }

[
   {
      "k" : "item",
      "v" : "foo"
   },
   {
      "k" : "qty",
      "v" : 25
   }
]

{ $objectToArray: {
    item: "foo",
    qty: 25,
    size: { len: 25, w: 10, uom: "cm" }
 } }

[
   {
      "k" : "item",
      "v" : "foo"
   },
   {
      "k" : "qty",
      "v" : 25
   },
   {
      "k" : "size",
      "v" : {
         "len" : 25,
         "w" : 10,
         "uom" : "cm"
      }
   }
]

示例

`$objectToArray` 例子

请考虑包含以下文档的 inventory 集合：

db.inventory.insertMany( [
   { _id: 1, item: "ABC1",  dimensions: { l: 25, w: 10, uom: "cm" } },
   { _id: 2, item: "ABC2",  dimensions: { l: 50, w: 25, uom: "cm" } },
   { _id: 3, item: "XYZ1",  dimensions: { l: 70, w: 75, uom: "cm" } }
] )

The following aggregation pipeline operation use the $objectToArray to return the dimensions field as an array:

db.inventory.aggregate(
   [
      {
         $project: {
            item: 1,
            dimensions: { $objectToArray: "$dimensions" }
         }
      }
   ]
)

该操作返回以下内容：

{ _id: 1, item: "ABC1", dimensions: [ { "k" : "l", "v" : 25 }, { "k" : "w", "v" : 10 }, { "k" : "uom", "v" : "cm" } ] }
{ _id: 2, item: "ABC2", dimensions: [ { "k" : "l", "v" : 50 }, { "k" : "w", "v" : 25 }, { "k" : "uom", "v" : "cm" } ] }
{ _id: 3, item: "XYZ1", dimensions: [ { "k" : "l", "v" : 70 }, { "k" : "w", "v" : 75 }, { "k" : "uom", "v" : "cm" } ] }

`$objectToArray` 对嵌套字段求和

请考虑包含以下文档的 inventory 集合：

db.inventory.insertMany( [
   { _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500 } }
   { _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200} }
] )

The following aggregation pipeline operation uses the $objectToArray along with $unwind and $group to calculate the total items in stock per warehouse.

db.inventory.aggregate([
   { $project: { warehouses: { $objectToArray: "$instock" } } },
   { $unwind: "$warehouses" },
   { $group: { _id: "$warehouses.k", total: { $sum: "$warehouses.v" } } }
])

该操作返回以下内容：

{ _id: "warehouse3", total: 200 }
{ _id: "warehouse2", total: 1000 }
{ _id: "warehouse1", total: 2500 }

`$objectToArray` +`$arrayToObject` 示例

考虑包含以下文档的 inventory 集合：

db.inventory.insertMany( [
   { _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500 } },
   { _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200},
   }
] )

以下聚合管道操作会计算每个商品的库存总额，并将其添加到 instock 文档：

db.inventory.aggregate( [
   { $addFields: { instock: { $objectToArray: "$instock" } } },
   { $addFields: { instock: { $concatArrays: [ "$instock", [ { "k": "total", "v": { $sum: "$instock.v" } } ] ] } } } ,
   { $addFields: { instock: { $arrayToObject: "$instock" } } }
] )

该操作返回以下内容：

{ _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500, total: 3000 } }
{ _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200, total: 700 } }

提示

$objectToArray（表达式操作符）

定义

行为

示例

$objectToArray 例子

$objectToArray 对嵌套字段求和

$objectToArray +$arrayToObject 示例

`$objectToArray` 例子

`$objectToArray` 对嵌套字段求和

`$objectToArray` +`$arrayToObject` 示例