适用对象：
MongoDB vCore
运算符 $toString 只是将表达式的值作为 String 返回。
语法
运算符的 $toString 语法为：
{ "$toString": <expression> }
参数
| 参数 | DESCRIPTION |
|---|---|
expression |
要转换为字符串值的指定值 |
例子
请查看 StoreData 数据库中 stores 集合的这个示例文档。
{
"_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
"name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
"location": {
"lat": -89.2384,
"lon": -46.4012
},
"staff": {
"totalStaff": {
"fullTime": 8,
"partTime": 20
}
},
"sales": {
"totalSales": 75670,
"salesByCategory": [
{
"categoryName": "Wine Accessories",
"totalSales": 34440
},
{
"categoryName": "Bitters",
"totalSales": 39496
},
{
"categoryName": "Rum",
"totalSales": 1734
}
]
},
"promotionEvents": [
{
"eventName": "Unbeatable Bargain Bash",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 6,
"Day": 23
},
"endDate": {
"Year": 2024,
"Month": 7,
"Day": 2
}
},
"discounts": [
{
"categoryName": "Whiskey",
"discountPercentage": 7
},
{
"categoryName": "Bitters",
"discountPercentage": 15
},
{
"categoryName": "Brandy",
"discountPercentage": 8
},
{
"categoryName": "Sports Drinks",
"discountPercentage": 22
},
{
"categoryName": "Vodka",
"discountPercentage": 19
}
]
},
{
"eventName": "Steal of a Deal Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 9,
"Day": 21
},
"endDate": {
"Year": 2024,
"Month": 9,
"Day": 29
}
},
"discounts": [
{
"categoryName": "Organic Wine",
"discountPercentage": 19
},
{
"categoryName": "White Wine",
"discountPercentage": 20
},
{
"categoryName": "Sparkling Wine",
"discountPercentage": 19
},
{
"categoryName": "Whiskey",
"discountPercentage": 17
},
{
"categoryName": "Vodka",
"discountPercentage": 23
}
]
}
]
}
示例 1：将 Double 值转换为字符串值
db.stores.aggregate([
{
"$match": {
"_id": "b0107631-9370-4acd-aafa-8ac3511e623d"
}
},
{
"$project": {
"originalLatitude": "$location.lat",
"latitudeAsString": {
"$toString": "$location.lat"
}
}
}])
此查询返回以下结果：
{
"_id": "b0107631-9370-4acd-aafa-8ac3511e623d",
"originalLatitude": 72.8377,
"latitudeAsString": "72.8377"
}
示例 2：将 Int 值转换为字符串值
db.stores.aggregate([
{
"$match": {
"_id": "b0107631-9370-4acd-aafa-8ac3511e623d"
}
},
{
"$project": {
"originalTotalSales": "$sales.totalSales",
"totalSalesAsString": {
"$toString": "$sales.totalSales"
}
}
}])
此查询返回以下结果：
{
"_id": "b0107631-9370-4acd-aafa-8ac3511e623d",
"originalTotalSales": 9366,
"totalSalesAsString": "9366"
}
此表根据输入值的数据类型来描述$toString运算符的预期行为。
| 值类型 | 行为/输出 |
|---|---|
| 布尔值为真 | 输出 -> “true” |
| 布尔值假 | 输出 -> “false” |
| 任何 Double、Int、Long 或 Decimal 类型的值。 例如，72 | 输出 -> “72” |
| 任何 ObjectId 值。 例如，ObjectId（“b010763193704acdaafa8ac3”） | 输出 -> “b010763193704acdaafa8ac3” |