$toLong (aggregation)¶

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

Definition定义¶

$toLong¶

~~New in version 4.0.~~版本4.0中的新功能。

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

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

{
   $toLong: <expression>
}

The $toLong takes any valid expression.

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

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

~~See also~~参阅

$convert

Behavior行为¶

The following table lists the input types that can be converted to a decimal:

The following table lists the input types that can be converted to a long:

Input Type	Behavior
Boolean	Returns NumberLong(0) for `false`. Returns NumberLong(1) for `true`.
Double	Returns truncated value. The truncated double value must fall within the minimum and maximum value for a long. You cannot convert a double value whose truncated value is less than the minimum long value or is greater than the maximum long value.
Decimal	Returns truncated value. The truncated decimal value must fall within the minimum and maximum value for a long. You cannot convert a decimal value whose truncated value is less than the minimum long value or is greater than the maximum long value.
Integer	Returns the int value as a long.
Long	No-op. Returns the long value.
String	Returns the numerical value of the string. The string value must be of a base₁₀ long (e.g. `"-5"`, `"123456"`). You cannot convert a string value of a float or decimal or non-base₁₀ number (e.g. `"-5.0"`, `"0x6400"`)
Date	Converts the Date into the number of milliseconds since the epoch.

The following table lists some conversion to long examples:

~~Example~~示例	~~Results~~结果
`{ $toLong: true }`	NumberLong(“1”)
`{ $toLong: false }`	NumberLong(“0”)
`{ $toLong: 1.99999 }`	NumberLong(“1”)
`{ $toLong: NumberDecimal("5.5000") }`	NumberLong(“5”)
`{ $toLong: NumberDecimal("9223372036854775808.0") }`	Error
`{ $toLong: NumberInt(8) }`	NumberLong(8)
`{ $toLong: ISODate("2018-03-26T04:38:28.044Z") }`	NumberLong(“1522039108044”)
`{ $toLong: "-2" }`	NumberLong(“-2”)
`{ $toLong: "2.5" }`	Error
`{ $toLong: null }`	null

Example示例¶

Create a collection orders with the following documents:

db.orders.insert( [
   { _id: 1, item: "apple", qty: NumberInt(5) },
   { _id: 2, item: "pie", qty: "100" },
   { _id: 3, item: "ice cream", qty: NumberLong(500) },
   { _id: 4, item: "almonds", qty: "50" },
] )

The following aggregation operation on the orders collection converts the qty to long before sorting by the value:

// Define stage to add convertedQty field with converted qty value

qtyConversionStage = {
   $addFields: {
      convertedQty: { $toLong: "$qty" }
   }
};

// Define stage to sort documents by the converted qty values

sortStage = {
   $sort: { "convertedQty": -1 }
};


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

The operation returns the following documents:

{ "_id" : 1, "item" : "apple", "qty" : 5, "convertedQty" : NumberLong(5) }
{ "_id" : 2, "item" : "pie", "qty" : "100", "convertedQty" : NumberLong(100) }
{ "_id" : 3, "item" : "ice cream", "qty" : NumberLong(500), "convertedQty" : NumberLong(500) }
{ "_id" : 4, "item" : "almonds", "qty" : "50", "convertedQty" : NumberLong(50) }

Note

If the conversion operation encounters an error, the aggregation operation stops and throws an error. To override this behavior, use $convert instead.