$arrayToObject (aggregation)

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Definition

将数组转换为单个文档；数组必须为：

[ [ "item", "abc123"], [ "qty", 25 ] ]

[ { "k": "item", "v": "abc123"}, { "k": "qty", "v": 25 } ]

$arrayToObject具有以下语法：

{ $arrayToObject: <expression> }

<expression>可以是解析为包含“ k”和“ v”字段的两元素数组或文档数组的任何有效expression。

有关表达式的更多信息，请参见Expressions。

Behavior

如果字段名称在数组中重复，

Example Results
{$ arrayToObject：{$ literal：[

{ "k": "item", "v": "abc123"},
{ "k": "qty", "v": 25 }
]}}		 { "item" : "abc123", "qty" : 25 }
{$ arrayToObject：{$ literal：[
[ "item", "abc123"], [ "qty", 25]
]}}		 { "item" : "abc123", "qty" : 25 }
{$ arrayToObject：{$ literal：[
100]}} { "item" : "abc123" }
从版本 3.6.10(和 3.4.19)开始，如果字段名称在数组中重复，则$arrayToObject使用该字段的最后一个值。

Examples

$arrayToObject Example

考虑包含以下文档的inventory集合：

{ "_id" : 1, "item" : "ABC1",  dimensions: [ { "k": "l", "v": 25} , { "k": "w", "v": 10 }, { "k": "uom", "v": "cm" } ] }
{ "_id" : 2, "item" : "ABC2",  dimensions: [ [ "l", 50 ], [ "w",  25 ], [ "uom", "cm" ] ] }
{ "_id" : 3, "item" : "ABC3",  dimensions: [ [ "l", 25 ], [ "l",  "cm" ], [ "l", 50 ] ] }

以下聚合管道操作使用$arrayToObject返回dimensions字段作为文档：

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

该操作返回以下内容：

{ "_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" : "ABC3", "dimensions" : { "l" : 50 } }

从版本 3.6.10(和 3.4.19)开始，如果字段名称在数组中重复，则$arrayToObject使用该字段的最后一个值。

$ objectToArray $ arrayToObject 示例

考虑包含以下文档的inventory集合：

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

以下聚合管道操作将计算每个物料的库存总量，并将其添加到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" } } }
] )

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 } }

See also

$objectToArray

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