$toInt (expression operator)（表达式运算符）

Definition定义

$toInt

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

$toInt has the following syntax:具有以下语法：

{
   $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表达式的简写：

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

Tip

$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：

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

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: Decimal128("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<定义阶段以添加转换价格和转换数量字段，其中包含转换价格和数量值</span>

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") }