$documentNumber (aggregation)

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Definition定义

New in version 5.0.在版本5.0中新增。

$documentNumber

Returns the position of a document (known as the document number) in the $setWindowFields stage partition.返回文档在$setWindowFields阶段分区中的位置（称为文档编号）。

The $setWindowFields stage sortBy field determines the document number. $setWindowFields阶段sortBy字段确定文档编号。For more information on how MongoDB compares fields with different types, see BSON comparison order.有关MongoDB如何比较不同类型字段的更多信息，请参阅BSON比较顺序。

$documentNumber returns a unique number for each document in a partition, even if multiple documents have identical sortBy field values in the partition.返回分区中每个文档的唯一编号，即使分区中有多个文档具有相同的sortBy字段值。

$documentNumber is only available in the $setWindowFields stage.仅在$setWindowFields阶段可用。

$documentNumber syntax:语法：

{ $documentNumber: { } }

$documentNumber does not accept any parameters.不接受任何参数。

Behavior行为

$documentNumber includes documents that have a sortBy field that is null or missing.包括sortBy字段为null或缺失的文档。

$documentNumber, $rank, and $denseRank return the position of the documents based on the sortBy field values.$documentNumber、$rank和$denseRank根据sortBy字段值返回文档的位置。

$documentNumber differs from $rank and $denseRank in how documents with identical sortBy field values in a partition are treated:$documentNumber与$rank和$denseRank的区别在于如何处理分区中具有相同sortBy字段值的文档：

  • $rank and 和$denseRank return the same position (known as the rank) for those documents.返回这些文档的相同位置（称为秩）。
  • $documentNumber returns a unique position (known as the document number) for those documents.返回这些文档的唯一位置（称为文档编号）。

See the example in Document Number for Duplicate, Null, and Missing Values.有关重复值、空值和缺失值，请参阅文档编号中的示例。

Examples示例

Document Number for Each State每个州的文档编号

Create a cakeSales collection that contains cake sales in the states of California (CA) and Washington (WA):创建包含加利福尼亚州（CA）和华盛顿州（WA）蛋糕销售的cakeSales系列：

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 }
] )

This example uses $documentNumber in the $setWindowFields stage to output the cake sales document number for each state:本示例使用$setWindowFields阶段中的$documentNumber输出每个州的蛋糕销售文档编号：

db.cakeSales.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { quantity: -1 },
         output: {
            documentNumberForState: {
               $documentNumber: {}
            }
         }
      }
   }
] )

In the example:在该示例中：

  • partitionBy: "$state" partitions the documents in the collection by state. 按州对集合中的文档进行分区。There are partitions for CA and WA.有用于CA和WA的分区。
  • sortBy: { quantity: -1 } sorts the documents in each partition by quantity in descending order (-1), so the highest quantity is first.按quantity按降序（-1）对每个分区中的文档进行排序，因此最高quantity为第一。
  • output sets the document number in a new field called documentNumberForState shown in the following results. 在名为documentNumberForState的新字段中设置文档编号，如下结果所示。documentNumberForState is unique within each state partition.在每个state分区内是唯一的。
{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "documentNumberForState" : 1 }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "documentNumberForState" : 2 }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "documentNumberForState" : 3 }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "documentNumberForState" : 1 }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "documentNumberForState" : 2 }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "documentNumberForState" : 3 }

Document Number for Duplicate, Null, and Missing Values重复值、空值和缺失值的文档编号

Create a cakeSalesWithDuplicates collection where:创建cakeSalesWithDuplicates集合，其中：

  • Cake sales are placed in the state of California (CA) and Washington (WA).蛋糕销售位于加利福尼亚州（CA）和华盛顿州（WA）。
  • Documents 6 to 8 have the same quantity and state as document 5.文档6至8具有与文档5相同的quantity和state。
  • Document 9 has the same quantity and state as document 4.文档9具有与文档4相同的quantity和state。
  • Document 10 has a null quantity.文档10的quantity为null。
  • Document 11 is missing the quantity.文档11缺少quantity。
db.cakeSalesWithDuplicates.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 },
   { _id: 6, type: "strawberry", orderDate: new Date("2020-01-08T06:12:03Z"),
     state: "WA", price: 41, quantity: 134 },
   { _id: 7, type: "strawberry", orderDate: new Date("2020-01-01T06:12:03Z"),
     state: "WA", price: 34, quantity: 134 },
   { _id: 8, type: "strawberry", orderDate: new Date("2020-01-02T06:12:03Z"),
     state: "WA", price: 40, quantity: 134 },
   { _id: 9, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39, quantity: 162 },
   { _id: 10, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39, quantity: null },
   { _id: 11, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39 }
] )

This example uses $documentNumber in the $setWindowFields stage to output the cakeSalesWithDuplicates document number for each state:本例使用$setWindowFields阶段中的$documentNumber输出每个州的cakeSalesWithDuplicates文档编号：

db.cakeSalesWithDuplicates.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { quantity: -1 },
         output: {
            documentNumberForState: {
               $documentNumber: {}
            }
         }
      }
   }
] )

In the example:在该示例中：

  • partitionBy: "$state" partitions the documents in the collection by state. 按州对集合中的文档进行分区。There are partitions for CA and WA.有用于CA和WA的分区。
  • sortBy: { quantity: -1 } sorts the documents in each partition by quantity in descending order (-1), so the highest quantity is first.按quantity按降序（-1）对每个分区中的文档进行排序，因此最高quantity为第一。
  • output sets the document number in a new field called documentNumberForState shown in the following results. 在名为documentNumberForState的新字段中设置文档编号，如下结果所示。documentNumberForState is unique within each state partition, and there are documentNumberForState values for documents with null quantity and missing quantity values.在每个state分区中是唯一的，并且对于quantity为null和quantity值缺失的文档，存在documentNumberForState值。
{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "documentNumberForState" : 1 }
{ "_id" : 9, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "quantity" : 162, "documentNumberForState" : 2 }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "documentNumberForState" : 3 }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "documentNumberForState" : 4 }
{ "_id" : 10, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "quantity" : null, "documentNumberForState" : 5 }
{ "_id" : 11, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "documentNumberForState" : 6 }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "documentNumberForState" : 1 }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "documentNumberForState" : 2 }
{ "_id" : 6, "type" : "strawberry", "orderDate" : ISODate("2020-01-08T06:12:03Z"),
  "state" : "WA", "price" : 41, "quantity" : 134, "documentNumberForState" : 3 }
{ "_id" : 7, "type" : "strawberry", "orderDate" : ISODate("2020-01-01T06:12:03Z"),
  "state" : "WA", "price" : 34, "quantity" : 134, "documentNumberForState" : 4 }
{ "_id" : 8, "type" : "strawberry", "orderDate" : ISODate("2020-01-02T06:12:03Z"),
  "state" : "WA", "price" : 40, "quantity" : 134, "documentNumberForState" : 5 }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "documentNumberForState" : 6 }
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