$toDate (aggregation)¶

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~~Definition~~定义
~~Behavior~~行为
~~Example~~示例

Definition定义¶

$toDate¶

~~New in version 4.0.~~版本4.0中的新功能。

Converts a value to a date. If the value cannot be converted to a date, $toDate errors. If the value is null or missing, $toDate returns null.

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

{
   $toDate: <expression>
}

The $toDate takes any valid expression.

The $toDate is a shorthand for the following $convert expression:

{ $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:

Input Type	Behavior
Double	Returns a date that corresponds to the number of milliseconds represented by the truncated double value. Positive number corresponds to the number of milliseconds since Jan 1, 1970. Negative number corresponds to the number of milliseconds before Jan 1, 1970.
Decimal	Returns a date that corresponds to the number of milliseconds represented by the truncated decimal value. Positive number corresponds to the number of milliseconds since Jan 1, 1970. Negative number corresponds to the number of milliseconds before Jan 1, 1970.
Long	Returns a date that corresponds to the number of milliseconds represented by the long value. Positive number corresponds to the number of milliseconds since Jan 1, 1970. Negative number corresponds to the number of milliseconds before Jan 1, 1970.
String	Returns a date that corresponds to the date string. The string must be a valid date string, such as: “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.

The following table lists some conversion to date examples:

~~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:

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:

// 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:

{ "_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. To override this behavior, use $convert instead.