$currentDate¶

Definition定义¶

$currentDate¶

The $currentDate operator sets the value of a field to the current date, either as a Date or a timestamp. $currentDate运算符将字段的值设置为当前日期（作为Date或timestamp）。The default type is Date.默认类型为Date。

The $currentDate operator has the form:$currentDate运算符的格式为：

{ $currentDate: { <field1>: <typeSpecification1>, ... } }

<typeSpecification> can be either:可以是以下两种之一：

• a boolean true to set the field value to the current date as a Date, or布尔值true，用于将字段值设置为当前日期，形式为Date，或
• a document { $type: "timestamp" } or { $type: "date" } which explicitly specifies the type. 明确指定类型的文档{ $type: "timestamp" }或{ $type: "date" }。The operator is case-sensitive and accepts only the lowercase "timestamp" or the lowercase "date".运算符区分大小写，只接受小写的"timestamp"或小写的"date"。

To specify a <field> in an embedded document or in an array, use dot notation.若要在嵌入式文档或数组中指定一个<field>，请使用点表示法。

Behavior行为¶

If the field does not exist, $currentDate adds the field to a document.如果该字段不存在，$currentDate将该字段添加到文档中。

Example示例¶

Create a sample collection customers with the following document:使用以下文档创建customers集合：

db.customers.insertOne(
   { _id: 1, status: "a", lastModified: ISODate("2013-10-02T01:11:18.965Z") }
)

The following operation updates the lastModified field to the current date, the "cancellation.date" field to the current timestamp as well as updating the status field to "D" and the "cancellation.reason" to "user request".以下操作将lastModified字段更新为当前日期，将"cancellation.date"字段更新为当前时间戳，并将status字段更新为"D"，将"cancellation.reason"更新为"user request"。

db.customers.updateOne(
   { _id: 1 },
   {
     $currentDate: {
        lastModified: true,
        "cancellation.date": { $type: "timestamp" }
     },
     $set: {
        "cancellation.reason": "user request",
        status: "D"
     }
   }
)

After the operation, you can query the collection to verify the update:操作完成后，您可以查询集合以验证更新：

db.customers.find().pretty()

The updated document would resemble:更新后的文件类似于：

{
   "_id" : 1,
   "status" : "D",
   "lastModified" : ISODate("2020-01-22T21:21:41.052Z"),
   "cancellation" : {
      "date" : Timestamp(1579728101, 1),
      "reason" : "user request"
   }
}

db.customers.updateOne(
  { _id: 1 },
  [
   { $set: { lastModified: "$$NOW", cancellation: {date: "$$CLUSTER_TIME", reason: "user request"}, status: "D" } }
  ]
)

db.customers.find().pretty()

{
   "_id" : 1,
   "status" : "D",
   "lastModified" : ISODate("2020-01-22T21:02:18.994Z"),
   "cancellation" : {
      "date" : Timestamp(1579726934, 2),
      "reason" : "user request"
   }
}