Database Manual / Reference / Query Language / Expressions

$objectToArray (aggregation)（聚合）

Definition定义

$objectToArray

Converts a document to an array. The return array contains an element for each field/value pair in the original document. Each element in the return array is a document that contains two fields k and v:将文档转换为数组。返回数组包含原始文档中每个字段/值对的元素。返回数组中的每个元素都是一个文档，其中包含两个字段k和v：

  • The k field contains the field name in the original document.k字段包含原始文档中的字段名称。
  • The v field contains the value of the field in the original document.v字段包含原始文档中该字段的值。

$objectToArray has the following syntax:具有以下语法：

{ $objectToArray: <object> }

The <object> expression can be any valid expression as long as it resolves to a document object. <object>表达式可以是任何有效的表达式，只要它解析为文档对象即可。$objectToArray applies to the top-level fields of its argument. If the argument is a document that itself contains embedded document fields, the $objectToArray does not recursively apply to the embedded document fields.$objectToArray应用于其参数的顶级字段。如果参数是本身包含嵌入式文档字段的文档，则$objectToArray不会递归应用于嵌入式文档字段。

For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Example示例Results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"
      }
   }
]

Examples示例

$objectToArray Example示例

Consider a inventory collection with the following documents:考虑使用以下文件进行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 $objectToArray to return the dimensions field as an array:以下聚合管道操作使用$objectToArray将dimensions字段作为数组返回：

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

The operation returns the following: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 to Sum Nested Fields对嵌套字段求和

Consider a inventory collection with the following documents:考虑使用以下文件进行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 $group to calculate the total items in stock per warehouse.以下聚合管道操作使用$objectToArray以及$unflew和$group来计算每个仓库的inventory总量。

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

The operation returns the following:该操作返回以下内容：

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

$objectToArray + $arrayToObject Example示例

Consider an inventory collection with the following documents:考虑使用以下文件进行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 calculates the total in stock for each item and adds to the instock document:以下聚合管道操作计算每个项目的总inventory，并添加到instock文档中：

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

The operation returns the following: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 } }

Tip

$arrayToObject