$month (aggregation)

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Definition定义

$month

Returns the month of a date as a number between 1 and 12.以1到12之间的数字返回日期的月份。

The $month expression has the following operator expression syntax:$month表达式具有以下运算符表达式语法：

{ $month: <dateExpression> }

Changed in version 3.6.在版本3.6中更改。

The argument must be a valid expression that resolves to one of the following:参数必须是解析为以下之一的有效表达式：

  • A Date, a Timestamp, or an ObjectID.
  • A document of the following form:

    New in version 3.6.版本3.6中的新功能。

    { date: <dateExpression>, timezone: <tzExpression> }
    Field字段Description描述
    date The date to which the operator is applied. <dateExpression> must be a valid expression that resolves to a Date, a Timestamp, or an ObjectID.
    timezone

    Optional. The timezone of the operation result. <tzExpression> must be a valid expression that resolves to a string formatted as either an Olson Timezone Identifier or a UTC Offset. If no timezone is provided, the result is displayed in UTC.

    FormatExamples
    Olson Timezone Identifier 
    "America/New_York"
"Europe/London"
"GMT"
    UTC Offset 
    +/-[hh]:[mm], e.g. "+04:45"
+/-[hh][mm], e.g. "-0530"
+/-[hh], e.g. "+03"

Behavior行为

Example示例Result
 
{ $month: new Date("2016-01-01") }
 1
{ $month: { date: new Date("Nov 7, 2003") } }
 11
{ $month: ISODate("2000-01-01T00:00:00Z") }
 1
{ $month: {
    date: new Date("August 14, 2011"),
    timezone: "America/Chicago"
} }
 8
{ $month: {
    date: ISODate("2000-01-01T00:00:00Z"),
    timezone: "-0500"
} }
 12
{ $month: "March 28, 1976" }
 error
{ $month: {
    date: Date("2016-01-01"),
    timezone: "-0500"
} }
 error
{ $month: "2009-04-09" }
 error

Note

$month cannot take a string as an argument.不能将字符串作为参数。

Example示例

Consider a sales collection with the following document:考虑一个包含以下文档的sales集合：

{
  "_id" : 1,
  "item" : "abc",
  "price" : 10,
  "quantity" : 2,
  "date" : ISODate("2014-01-01T08:15:39.736Z")
}

The following aggregation uses the $month and other date operators to break down the date field:以下聚合使用$month和其他日期运算符来分解日期字段：

db.sales.aggregate(
   [
     {
       $project:
         {
           year: { $year: "$date" },
month: { $month: "$date" },           day: { $dayOfMonth: "$date" },
           hour: { $hour: "$date" },
           minutes: { $minute: "$date" },
           seconds: { $second: "$date" },
           milliseconds: { $millisecond: "$date" },
           dayOfYear: { $dayOfYear: "$date" },
           dayOfWeek: { $dayOfWeek: "$date" },
           week: { $week: "$date" }
         }
     }
   ]
)

The operation returns the following result:操作返回以下结果：

{
  "_id" : 1,
  "year" : 2014,
  "month" : 1,
  "day" : 1,
  "hour" : 8,
  "minutes" : 15,
  "seconds" : 39,
  "milliseconds" : 736,
  "dayOfYear" : 1,
  "dayOfWeek" : 4,
  "week" : 0
}