$toInt (aggregation)

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Definition定义

$toInt

New in version 4.0.版本4.0中的新功能。

Converts a value to an integer. If the value cannot be converted to an integer, $toInt errors. If the value is null or missing, $toInt returns null.

$toInt has the following syntax:语法如下所示：

{
   $toInt: <expression>
}

The $toInt takes any valid expression.

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

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

See also参阅

$convert

Behavior行为

The following table lists the input types that can be converted to an integer:

Input TypeBehavior
Boolean
Returns 0 for false.
Returns 1 for true.
Double

Returns truncated value.

The truncated double value must fall within the minimum and maximum value for an integer.

You cannot convert a double value whose truncated value is less than the minimum integer value or is greater than the maximum integer value.

Decimal

Returns truncated value.

The truncated decimal value must fall within the minimum and maximum value for an integer.

You cannot convert a decimal value whose truncated value is less than the minimum integer value or is greater than the maximum integer value.

Integer No-op. Returns the integer value.
Long

Returns the long value as an integer.

The long value must fall within the minimum and maximum value for an integer.

You cannot convert a long value that is less than the minimum integer value or is greater than the maximum integer value.

String

Returns the numerical value of the string as an integer.

The string value must be a base10 integer; e.g. "-5", "123456").

You cannot convert a string value of a float or decimal or non-base10 number (e.g. "-5.0", "0x6400")

The following table lists some conversion to integer examples:

Example示例Results结果
$toInt: true 1
$toInt: false 0
$toInt: 1.99999 1
$toInt: NumberDecimal("5.5000") 5
$toInt: NumberDecimal("9223372036000.000") Error
$toInt: NumberLong("5000") 5000
$toInt: NumberLong("922337203600") Error
$toInt: "-2" -2
$toInt: "2.5" Error
$toInt: null null

Example示例

Create a collection orders with the following documents:

db.orders.insert( [
   { _id: 1, item: "apple", qty: 5, price: 10 },
   { _id: 2, item: "pie", qty: 10, price: NumberDecimal("20.0") },
   { _id: 3, item: "ice cream", qty: 2, price: "4.99" },
   { _id: 4, item: "almonds" ,  qty: 5, price: 5 }
] )

The following aggregation operation on the orders collection converts the qty to an integer as well as convert price to a decimal before calculating the total price:

// Define stage to add convertedPrice and convertedQty fields with the converted price and qty values

priceQtyConversionStage = {
   $addFields: {
      convertedPrice: { $toDecimal: "$price" },
      convertedQty: { $toInt: "$qty" },
   }
};

// Define stage to calculate total price by multiplying convertedPrice and convertedQty fields


totalPriceCalculationStage = {
   $project: { item: 1, totalPrice: { $multiply: [ "$convertedPrice", "$convertedQty" ] } }
};

db.orders.aggregate( [
   priceQtyConversionStage,
   totalPriceCalculationStage
])

The operation returns the following documents:

{ "_id" : 1, "item" : "apple", "totalPrice" : NumberDecimal("50.0000000000000") }
{ "_id" : 2, "item" : "pie", "totalPrice" : NumberDecimal("200.0") }
{ "_id" : 3, "item" : "ice cream", "totalPrice" : NumberDecimal("9.98") }
{ "_id" : 4, "item" : "almonds", "totalPrice" : NumberDecimal("25.00000000000000") }

Note

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