$toDate (aggregation)

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Definition定义

$toDate

New in version 4.0.版本4.0中的新功能。

Converts a value to a date. 将值转换为日期。If the value cannot be converted to a date, $toDate errors. 如果该值无法转换为日期，$toDate错误。If the value is null or missing, $toDate returns null.如果值为null或缺失，$toDate返回null。

$toDate has the following syntax:语法如下所示：

{
   $toDate: <expression>
}

The $toDate takes any valid expression.$toDate接受任何有效表达式。

The $toDate is a shorthand for the following $convert expression:$toDate是以下$convert表达式的简写形式：

{ $convert: { input: <expression>, to: "date" } }

See also参阅

$convert and $dateFromString

Behavior行为

The following table lists the input types that can be converted to a date:下表列出了可以转换为日期的输入类型：

Input TypeBehavior
Double

Returns a date that corresponds to the number of milliseconds represented by the truncated double value.返回与截断的双精度值表示的毫秒数相对应的日期。

Positive number corresponds to the number of milliseconds since Jan 1, 1970.正数对应自1970年1月1日以来的毫秒数。

Negative number corresponds to the number of milliseconds before Jan 1, 1970.负数对应1970年1月1日之前的毫秒数。

Decimal

Returns a date that corresponds to the number of milliseconds represented by the truncated decimal value.返回与截断的十进制值表示的毫秒数相对应的日期。

Positive number corresponds to the number of milliseconds since Jan 1, 1970.正数对应自1970年1月1日以来的毫秒数。

Negative number corresponds to the number of milliseconds before Jan 1, 1970.负数对应1970年1月1日之前的毫秒数。

Long

Returns a date that corresponds to the number of milliseconds represented by the long value.返回与long值表示的毫秒数相对应的日期。

Positive number corresponds to the number of milliseconds since Jan 1, 1970.正数对应自1970年1月1日以来的毫秒数。

Negative number corresponds to the number of milliseconds before Jan 1, 1970.负数对应1970年1月1日之前的毫秒数。

String

Returns a date that corresponds to the date string.返回与日期字符串相对应的日期。

The string must be a valid date string, such as:该字符串必须是有效的日期字符串，例如：

  • “2018-03-03”
  • “2018-03-03T12:00:00Z”
  • “2018-03-03T12:00:00+0500”
ObjectId Returns a date that corresponds to the timestamp of the ObjectId.返回与ObjectId的时间戳相对应的日期。

The following table lists some conversion to date examples:下表列出了一些到日期的转换示例：

Example示例Results结果
{$toDate: 120000000000.5} ISODate(“1973-10-20T21:20:00Z”)
{$toDate: NumberDecimal("1253372036000.50")} ISODate(“2009-09-19T14:53:56Z”)
{$toDate: NumberLong("1100000000000")} ISODate(“2004-11-09T11:33:20Z”)
{$toDate:  NumberLong("-1100000000000")} ISODate(“1935-02-22T12:26:40Z”)
{$toDate: ObjectId("5ab9c3da31c2ab715d421285")} ISODate(“2018-03-27T04:08:58Z”)
{$toDate:  "2018-03-03"} ISODate(“2018-03-03T00:00:00Z”)
{$toDate: "2018-03-20 11:00:06 +0500"} ISODate(“2018-03-20T06:00:06Z”)
{$toDate: "Friday"} Error

Example示例

Create a collection orders with the following documents:使用以下文档创建集合orders：

db.orders.insert( [
   { _id: 1, item: "apple", qty: 5, order_date: new Date("2018-03-10") },
   { _id: 2, item: "pie", qty: 10,  order_date: new Date("2018-03-12")},
   { _id: 3, item: "ice cream", qty: 2, price: "4.99", order_date: "2018-03-05" },
   { _id: 4, item: "almonds" ,  qty: 5, price: 5,  order_date: "2018-03-05 +10:00"}
] )

The following aggregation operation on the orders collection converts the order_date to date before sorting by the date value:orders集合上的以下聚合操作将order_date转换为按日期值排序之前的日期：

// Define stage to add convertedDate field with the converted order_date value

dateConversionStage = {
   $addFields: {
      convertedDate: { $toDate: "$order_date" }
   }
};

// Define stage to sort documents by the converted date

sortStage = {
   $sort: { "convertedDate": 1 }
};

db.orders.aggregate( [
   dateConversionStage,
   sortStage
])

The operation returns the following documents:该操作返回以下文档：

{ "_id" : 4, "item" : "almonds", "qty" : 5, "price" : 5, "order_date" : "2018-03-05 +10:00", "convertedDate" : ISODate("2018-03-04T14:00:00Z") }
{ "_id" : 3, "item" : "ice cream", "qty" : 2, "price" : "4.99", "order_date" : "2018-03-05", "convertedDate" : ISODate("2018-03-05T00:00:00Z") }
{ "_id" : 1, "item" : "apple", "qty" : 5, "order_date" : ISODate("2018-03-10T00:00:00Z"), "convertedDate" : ISODate("2018-03-10T00:00:00Z") }
{ "_id" : 2, "item" : "pie", "qty" : 10, "order_date" : ISODate("2018-03-12T00:00:00Z"), "convertedDate" : ISODate("2018-03-12T00:00:00Z") }

Note

If the conversion operation encounters an error, the aggregation operation stops and throws an error. 如果转换操作遇到错误，聚合操作将停止并抛出错误。To override this behavior, use $convert instead.若要重写此行为，请改用$convert。