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推入（聚合）

在本页

  • 定义
  • 语法
  • 行为
  • 示例

定义

$push

$push返回应用表达式到文档的结果的所有值组成的数组。表达式。

$push在这些阶段可用

语法

$push语法

{ $push: <expression> }

有关表达式的更多信息，请参阅表达式运算符。

行为

在聚合管道的 $push 阶段使用时，进入管道的文档顺序决定了输出数组中文档的顺序。为了确保顺序确定，应该在 $group 管道阶段之后跟随一个 $sort 阶段。

示例

在 $group 阶段中使用

考虑一个包含以下文档的 sales 集合

{ "_id" : 1, "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") }
{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") }
{ "_id" : 3, "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") }
{ "_id" : 4, "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") }
{ "_id" : 5, "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") }
{ "_id" : 6, "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-15T12:05:10Z") }
{ "_id" : 7, "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T14:12:12Z") }

根据日期字段的日和年分组文档，以下操作使用$push累加器计算每个组的物品和销售数量列表

db.sales.aggregate(
   [
   { $sort: { date: 1, item: 1 } },
   {
       $group:
         {
           _id: { day: { $dayOfYear: "$date"}, year: { $year: "$date" } },
           itemsSold: { $push:  { item: "$item", quantity: "$quantity" } }
         }
     }
   ]
)

操作返回以下结果

{
   "_id" : { "day" : 46, "year" : 2014 },
   "itemsSold" : [
      { "item" : "abc", "quantity" : 10 },
      { "item" : "xyz", "quantity" : 10 },
      { "item" : "xyz", "quantity" : 5 },
      { "item" : "xyz", "quantity" : 10 }
   ]
}
{
   "_id" : { "day" : 34, "year" : 2014 },
   "itemsSold" : [
      { "item" : "jkl", "quantity" : 1 },
      { "item" : "xyz", "quantity" : 5 }
   ]
}
{
   "_id" : { "day" : 1, "year" : 2014 },
   "itemsSold" : [ { "item" : "abc", "quantity" : 2 } ]
}

在
阶段中使用

新版本中5.0.

创建一个包含加利福尼亚（CA）和华盛顿（WA）各州糕点销售的cakeSales集合

db.cakeSales.insertMany( [
   { _id: 0, type: "chocolate", orderDate: new Date("2020-05-18T14:10:30Z"),
     state: "CA", price: 13, quantity: 120 },
   { _id: 1, type: "chocolate", orderDate: new Date("2021-03-20T11:30:05Z"),
     state: "WA", price: 14, quantity: 140 },
   { _id: 2, type: "vanilla", orderDate: new Date("2021-01-11T06:31:15Z"),
     state: "CA", price: 12, quantity: 145 },
   { _id: 3, type: "vanilla", orderDate: new Date("2020-02-08T13:13:23Z"),
     state: "WA", price: 13, quantity: 104 },
   { _id: 4, type: "strawberry", orderDate: new Date("2019-05-18T16:09:01Z"),
     state: "CA", price: 41, quantity: 162 },
   { _id: 5, type: "strawberry", orderDate: new Date("2019-01-08T06:12:03Z"),
     state: "WA", price: 43, quantity: 134 }
] )

此示例在$setWindowFields阶段中使用$push，以输出每个state的糕点销售quantity值数组

db.cakeSales.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { orderDate: 1 },
         output: {
            quantitiesForState: {
               $push: "$quantity",
               window: {
                  documents: [ "unbounded", "current" ]
               }
            }
         }
      }
   }
] )

在示例中

  • partitionBy: "$state" 分区集合中的文档，按state进行分区。有CA和WA的分区。

  • sortBy: { orderDate: 1 } 排序每个分区中的文档，按orderDate升序（1），因此最早的orderDate排在第一位。

  • output使用$push设置文档窗口中的quantity值数组。

    窗口包含从unbounded下限到输出中当前文档之间的文档。这意味着$push将quantity值追加到从分区开始到当前文档之间的文档的quantitiesForState数组中。

在此输出中，CA和WA的quantity值数组显示在quantitiesForState数组中

{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "quantitiesForState" : [ 162 ] }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "quantitiesForState" : [ 162, 120 ] }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "quantitiesForState" : [ 162, 120, 145 ] }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "quantitiesForState" : [ 134 ] }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "quantitiesForState" : [ 134, 104 ] }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "quantitiesForState" : [ 134, 104, 140 ] }

返回

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