$tsIncrement (aggregation)

以下も参照してください。

Obtain the Incrementing Ordinal from a Timestamp Field

会社の株式金融マーケットの売上情報を含むstockSalesコレクションを作成します。

db.stockSales.insertMany( [
   { _id: 0, symbol: "MDB", saleTimestamp: Timestamp(1622731060, 1) },
   { _id: 1, symbol: "MDB", saleTimestamp: Timestamp(1622731060, 2) },
   { _id: 2, symbol: "MSFT", saleTimestamp: Timestamp(1714124193, 1) },
   { _id: 3, symbol: "MSFT", saleTimestamp: Timestamp(1714124193, 2) },
   { _id: 4, symbol: "MSFT", saleTimestamp: Timestamp(1714124193, 3) }
] )

タイムスタンプコンストラクター内で、 は次の操作を行います。

• 最初の値は、 UNIX エポックからの経過秒数です。

• 2 番目の値は、増分序数です。 同じ秒内に複数のイベントが発生した場合、増分序数は各イベントを一意に識別します。

The following example uses $tsIncrement in a $project stage to return the incrementing ordinal from the stock sales saleTimestamp field:

db.stockSales.aggregate( [
   {
      $project:
      {
         _id: 0, saleTimestamp: 1, saleIncrement: { $tsIncrement: "$saleTimestamp" }
      }
   }
] )

In the example, $project only includes the saleTimestamp and saleIncrement fields as shown in the following output:

{
  saleTimestamp: Timestamp({ t: 1622731060, i: 1 }),
  saleIncrement: Long("1")
},
{
  saleTimestamp: Timestamp({ t: 1622731060, i: 2 }),
  saleIncrement: Long("2")
},
{
  saleTimestamp: Timestamp({ t: 1714124193, i: 1 }),
  saleIncrement: Long("1")
},
{
  saleTimestamp: Timestamp({ t: 1714124193, i: 2 }),
  saleIncrement: Long("2")
},
{
  saleTimestamp: Timestamp({ t: 1714124193, i: 3 }),
  saleIncrement: Long("3")
}

変更ストリーム カーソルで$tsIncrementを使用してコレクションの変更を監視

The example in this section uses $tsIncrement in a change stream cursor to return every other change made to a collection in the same second of time.

このセクションの後半では、 cakeSalesという名前のコレクションに変更ストリーム カーソルを作成します。

cakeSalesCursor = db.cakeSales.watch( [
   {
      $match: {
         $expr: {
            $eq: [
               { $mod: [ { $tsIncrement: "$clusterTime" } , 2 ] },
               0
            ]
         }
      }
   }
] )

この例では、次のことは行われません。

• db.collection.watch()メソッドは、 cakeSalesコレクションの変更ストリーム カーソルを作成し、そのカーソルをcakeSalesCursorに保存します。

• $match stage filters the documents to those returned by the $expr operator.

• $expr operator:

  • Applies $mod 2 to the $clusterTime variable's incrementing ordinal returned by $tsIncrement.

    $clusterTime is the timestamp from the oplog entry when the cakeSales collection is modified. See Command Response.

  • Compares the returned value from $mod to 0 using $eq.

カリフォルニア州（CA）とワシントン州（WA）のケーキ販売を含む cakeSales コレクションを作成します。

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 }
] )

cakeSalesコレクションの変更をモニターするには、 cakeSalesCursorを使用します。 たとえば、 cakeSalesCursorから次のドキュメントを取得するには、 next()メソッドを使用します。

cakeSalesCursor.next()

Depending on the second when the documents were added to cakeSales, the output from cakeSalesCursor.next() varies. For example, the document additions might span more than one second.

The following cakeSalesCursor.next() example output shows the insert details for the first document added to the cakeSales collection. Notice the incrementing ordinal i is 2 in the clusterTime field.

_id: {
  _data: '82613A4F25000000022B022C0100296E5A100454C5BFAF538C47AB950614F43889BE00461E5F696400290004'
},
operationType: 'insert',
clusterTime: Timestamp({ t: 1631211301, i: 2 }),
fullDocument: {
  _id: 0,
  type: 'chocolate',
  orderDate: ISODate("2020-05-18T14:10:30.000Z"),
  state: 'CA',
  price: 13,
  quantity: 120
},
ns: { db: 'test', coll: 'cakeSales' },
documentKey: { _id: 0 }

Running cakeSalesCursor.next() again returns the cakeSales document for which the clusterTime incrementing ordinal i is 4, omitting the document where i is 3.