$dateToString (aggregation)

Definition定义

$dateToString

Converts a date object to a string according to a user-specified format.根据用户指定的格式将日期对象转换为字符串。

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

{ $dateToString: {
    date: <dateExpression>,
    format: <formatString>,
    timezone: <tzExpression>,
    onNull: <expression>
} }

The $dateToString takes a document with the following fields:$dateToString获取具有以下字段的文档：

Field字段	Description描述
date	Changed in version 3.6.在版本3.6中更改。 The date to convert to string. <dateExpression> must be a valid expression that resolves to a Date, a Timestamp, or an ObjectID.要转换为字符串的日期<dateExpression>必须是解析为Date、Timestamp或ObjectID的有效表达式。
format	Optional. 可选。The date format specification. 日期格式规范。<formatString> can be any string literal, containing 0 or more format specifiers. 可以是任何字符串文字，包含0个或多个格式说明符。For a list of specifiers available, see Format Specifiers.有关可用说明符的列表，请参阅格式说明符。 If unspecified, $dateToString uses "%Y-%m-%dT%H:%M:%S.%LZ" as the default format.如果未指定，$dateToString使用"%Y-%m-%dT%H:%M:%S.%LZ"作为默认格式。 Changed in version 4.0.在版本4.0中更改。 The format field is optional if featureCompatibilityVersion (fCV) is set to "4.0" or greater. 如果featureCompatibilityVersion(fCV)设置为“4.0”或更高，则format字段是可选的。For more information on fCV, see setFeatureCompatibilityVersion.有关fCV的更多信息，请参阅setFeatureCompatibilityVersion。
timezone	Optional. 可选。The timezone of the operation result. 操作结果的时区。<tzExpression> must be a valid expression that resolves to a string formatted as either an Olson Timezone Identifier or a UTC Offset. <tzExpression>必须是有效的表达式，可以解析为格式为奥尔森时区标识符或UTC偏移量的字符串。If no timezone is provided, the result is displayed in UTC.如果未提供timezone，结果将以UTC显示。 Format Examples Olson Timezone Identifier奥尔森时区标识符 "America/New_York" "Europe/London" "GMT" UTC Offset +/-[hh]:[mm], e.g. "+04:45" +/-[hh][mm], e.g. "-0530" +/-[hh], e.g. "+03"
onNull	Optional. 可选。The value to return if the date is null or missing. 如果date为空或缺失，则返回的值。The arguments can be any valid expression.参数可以是任何有效的表达式。 If unspecified, $dateToString returns null if the date is null or missing.如果未指定，$dateToString在日期为空或缺失时返回空。 New in version 4.0.在版本4.0中新增。 Requires featureCompatibilityVersion (fCV) set to "4.0" or greater. 需要将featureCompatibilityVersion(fCV)设置为“4.0”或更高。For more information on fCV, see setFeatureCompatibilityVersion.有关fCV的更多信息，请参阅setFeatureCompatibilityVersion。

Format Specifiers格式说明符

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

Example示例

Consider a sales collection with the following document:考虑具有以下文档的sales集合：

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

The following aggregation uses $dateToString to return the date field as formatted strings:以下聚合使用$dateToString以格式化字符串的形式返回date字段：

db.sales.aggregate(
   [
     {
       $project: {
          yearMonthDayUTC: { $dateToString: { format: "%Y-%m-%d", date: "$date" } },
          timewithOffsetNY: { $dateToString: { format: "%H:%M:%S:%L%z", date: "$date", timezone: "America/New_York"} },
          timewithOffset430: { $dateToString: { format: "%H:%M:%S:%L%z", date: "$date", timezone: "+04:30" } },
          minutesOffsetNY: { $dateToString: { format: "%Z", date: "$date", timezone: "America/New_York" } },
          minutesOffset430: { $dateToString: { format: "%Z", date: "$date", timezone: "+04:30" } }
       }
     }
   ]
)

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

{
   "_id" : 1,
   "yearMonthDayUTC" : "2014-01-01",
   "timewithOffsetNY" : "03:15:39:736-0500",
   "timewithOffset430" : "12:45:39:736+0430",
   "minutesOffsetNY" : "-300",
   "minutesOffset430" : "270"
}