$dateFromString (aggregation)¶

Definition定义¶

$dateFromString¶

New in version 3.6.版本3.6中的新功能。

Converts a date/time string to a date object.将日期/时间字符串转换为日期对象。

The $dateFromString expression has the following syntax:$dateFromString表达式语法如下所示：

{ $dateFromString: {
     dateString: <dateStringExpression>,
     format: <formatStringExpression>,
     timezone: <tzExpression>,
     onError: <onErrorExpression>,
     onNull: <onNullExpression>
} }

The $dateFromString takes a document with the following fields:$dateFromString采用带有以下字段的文档

Field字段	Description描述
dateString	The date/time string to convert to a date object. 要转换为日期对象的日期/时间字符串。See Date for more information on date/time formats.有关日期/时间格式的更多信息，请参阅Date。 Note If specifying the timezone option to the operator, do not include time zone information in the dateString.如果为运算符指定timezone选项，请不要在dateString中包含时区信息。
format	Optional.可选。The date format specification of the dateString. dateString的日期格式规范。The format can be any expression that evaluates to a string literal, containing 0 or more format specifiers. format可以是任何计算结果为字符串文字的表达式，其中包含0个或多个格式说明符。For a list of specifiers available, see Format Specifiers.有关可用的说明符列表，请参阅格式说明符。 If unspecified, $dateFromString uses "%Y-%m-%dT%H:%M:%S.%LZ" as the default format.如果未指定，$dateFromString使用"%Y-%m-%dT%H:%M:%S.%LZ"作为默认格式。 New in version 4.0.版本4.0中的新功能。
timezone	Optional.可选。The time zone to use to format the date.用于设置日期格式的时区。 Note If the dateString argument is formatted like ‘2017-02-08T12:10:40.787Z’, in which the ‘Z’ at the end indicates Zulu time (UTC time zone), you cannot specify the timezone argument.如果dateString参数的格式类似于“2017-02-08T12:10:40.787Z”，其中末尾的“Z”表示祖鲁时间（UTC时区），则不能指定timezone参数。 <timezone> allows for the following options and expressions that evaluate to them:允许使用以下选项和表达式进行计算： an Olson Timezone Identifier, such as "Europe/London" or "America/New_York", or奥尔森时区标识符，如"Europe/London"或"America/New_York"，或 a UTC offset in the form:UTC偏移量的形式如下： +/-[hh]:[mm], e.g. "+04:45", or +/-[hh][mm], e.g. "-0530", or +/-[hh], e.g. "+03", or The strings “Z”, “UTC”, or “GMT”字符串“Z”、“UTC”或“GMT” For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。
onError	Optional.可选。If $dateFromString encounters an error while parsing the given dateString, it outputs the result value of the provided onError expression. 如果$dateFromString在分析给定的dateString时遇到错误，它将输出提供的onError表达式的结果值。This result value can be of any type.此结果值可以是任何类型。 If you do not specify onError, $dateFromString throws an error if it cannot parse dateString.如果未指定onError，$dateFromString在无法分析dateString时抛出错误。
onNull	Optional.可选。If the dateString provided to $dateFromString is null or missing, it outputs the result value of the provided onNull expression. 如果提供给$dateFromString的dateString为null或缺失，它将输出提供的onNull表达式的结果值。This result value can be of any type.此结果值可以是任何类型。 If you do not specify onNull and dateString is null or missing, then $dateFromString outputs null.如果未指定onNull且dateString为null或缺失，则$dateFromString将输出null。

Behavior行为¶

{ $dateFromString: {
    dateString: "2017-02-08T12:10:40.787"
} }

{ $dateFromString: {
     dateString: "2017-02-08T12:10:40.787",
     timezone: "America/New_York"
} }

{ $dateFromString: {
     dateString: "2017-02-08"
} }

{ $dateFromString: {
     dateString: "06-15-2018",
     format: "%m-%d-%Y"
} }

{ $dateFromString: {
     dateString: "15-06-2018",
     format: "%d-%m-%Y"
} }

Format Specifiers格式说明符¶

The following format specifiers are available for use in the <formatString>:以下格式说明符可在<formatString>中使用：

Examples示例¶

{ _id: 1, date: "2017-02-08T12:10:40.787", timezone: "America/New_York", message:  "Step 1: Started" },
{ _id: 2, date: "2017-02-08", timezone: "-05:00", message:  "Step 1: Ended" },
{ _id: 3, message:  " Step 1: Ended " },
{ _id: 4, date: "2017-02-09", timezone: "Europe/London", message: "Step 2: Started"}
{ _id: 5, date: "2017-02-09T03:35:02.055", timezone: "+0530", message: "Step 2: In Progress"}

db.logmessages.aggregate( [ {
   $project: {
      date: {
         $dateFromString: {
            dateString: '$date',
            timezone: 'America/New_York'
         }
      }
   }
} ] )

{ "_id" : 1, "date" : ISODate("2017-02-08T17:10:40.787Z") }
{ "_id" : 2, "date" : ISODate("2017-02-08T05:00:00Z") }
{ "_id" : 3, "date" : null }
{ "_id" : 4, "date" : ISODate("2017-02-09T05:00:00Z") }
{ "_id" : 5, "date" : ISODate("2017-02-09T08:35:02.055Z") }

db.logmessages.aggregate( [ {
   $project: {
      date: {
         $dateFromString: {
            dateString: '$date',
            timezone: '$timezone'
         }
      }
   }
} ] )

{ "_id" : 1, "date" : ISODate("2017-02-08T17:10:40.787Z") }
{ "_id" : 2, "date" : ISODate("2017-02-08T05:00:00Z") }
{ "_id" : 3, "date" : null }
{ "_id" : 4, "date" : ISODate("2017-02-09T00:00:00Z") }
{ "_id" : 5, "date" : ISODate("2017-02-08T22:05:02.055Z") }

{ "_id" : 1, "date" : "2017-02-08T12:10:40.787", timezone: "America/New_York" },
{ "_id" : 2, "date" : "20177-02-09T03:35:02.055", timezone: "America/New_York" }

db.dates.aggregate( [ {
   $project: {
      date: {
         $dateFromString: {
            dateString: '$date',
            timezone: '$timezone',
            onError: '$date'
         }
      }
   }
} ] )

{ "_id" : 1, "date" : ISODate("2017-02-08T17:10:40.787Z") }
{ "_id" : 2, "date" : "20177-02-09T03:35:02.055" }

{ "_id" : 1, "date" : "2017-02-08T12:10:40.787", timezone: "America/New_York" },
{ "_id" : 2, "date" : null, timezone: "America/New_York" }

db.dates.aggregate( [ {
   $project: {
      date: {
         $dateFromString: {
            dateString: '$date',
            timezone: '$timezone',
            onNull: new Date(0)
         }
      }
   }
} ] )

{ "_id" : 1, "date" : ISODate("2017-02-08T17:10:40.787Z") }
{ "_id" : 2, "date" : ISODate("1970-01-01T00:00:00Z") }