$toInt (aggregation)

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Definition定义

$toInt

New in version 4.0.在版本4.0中新增。

Converts a value to an integer. 将值转换为整数。If the value cannot be converted to an integer, $toInt errors. 如果该值无法转换为整数，则$toInt会出错。If the value is null or missing, $toInt returns null.如果值为null或缺失，$toInt将返回null。

$toInt has the following syntax:语法如下：

{
   $toInt: <expression>
}

The $toInt takes any valid expression.$toInt接受任何有效表达式。

The $toInt is a shorthand for the following $convert expression:$toInt是以下$convert表达式的缩写：

{ $convert: { input: <expression>, to: "int" } }
Tip提示
See also: 参阅：

$convert

Behavior行为

The following table lists the input types that can be converted to an integer:下表列出了可以转换为整数的输入类型：

Input Type输入类型Behavior行为
Boolean

Returns 0 for false.如果为false，则返回0。

Returns 1 for true.如果为true，则返回1。

Double

Returns truncated value.返回截断值。

The truncated double value must fall within the minimum and maximum value for an integer.截断的双精度值必须在整数的最小值和最大值之间。

You cannot convert a double value whose truncated value is less than the minimum integer value or is greater than the maximum integer value.不能转换截断值小于最小整数值或大于最大整数值的双精度值。

Decimal

Returns truncated value.返回截断值。

The truncated decimal value must fall within the minimum and maximum value for an integer.截断的十进制值必须在整数的最小值和最大值之间。

You cannot convert a decimal value whose truncated value is less than the minimum integer value or is greater than the maximum integer value.不能转换截断值小于最小整数值或大于最大整数值的十进制值。

IntegerNo-op. Returns the integer value.无。返回整数值。
Long

Returns the long value as an integer.以整数形式返回长值。

The long value must fall within the minimum and maximum value for an integer.长值必须在整数的最小值和最大值之间。

You cannot convert a long value that is less than the minimum integer value or is greater than the maximum integer value.不能转换小于最小整数值或大于最大整数值的长值。

String

Returns the numerical value of the string as an integer.以整数形式返回字符串的数值。

The string value must be a base 10 integer; e.g. "-5", "123456").字符串值必须是以10为基数的整数；例如"-5"、"123456"）。

You cannot convert a string value of a float or decimal or non-base 10 number (e.g. "-5.0", "0x6400")不能转换浮点、十进制或非十进制数字的字符串值（例如"-5.0"、"0x6400"）

The following table lists some conversion to integer examples:下表列出了一些转换为整数的示例：

Example示例Results结果
$toInt: true1
$toInt: false0
$toInt: 1.999991
$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: nullnull

Example示例

Create a collection orders with the following documents:使用以下文档创建集合orders：

db.orders.insertMany( [
   { _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:以下聚合操作：

  • converts qty to an integer,将qty转换为整数，
  • converts price to a decimal,将price转换为小数，
  • calculates the total price:计算总价：
// 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:该操作返回以下文档：

{ _id: 1, item: 'apple', totalPrice: Decimal128("50") },
{ _id: 2, item: 'pie', totalPrice: Decimal128("200.0") },
{ _id: 3, item: 'ice cream', totalPrice: Decimal128("9.98") },
{ _id: 4, item: 'almonds', totalPrice: Decimal128("25") }
Note注意

If the conversion operation encounters an error, the aggregation operation stops and throws an error. 如果转换操作遇到错误，聚合操作将停止并抛出错误。To override this behavior, use $convert instead.要覆盖此行为，请改用$convert。

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