$bsonSize 运算符用于在编码为 BSON 时以字节为单位返回文档的大小。 这对于理解 MongoDB 集合中文档的存储要求非常有用。 该运算符可在聚合管道中使用，以计算文档的大小，这有助于优化存储和了解性能影响。
语法
{ $bsonSize: <expression> }
parameters
| 说明 | |
|---|---|
<expression> |
解析为要计算其 BSON 大小的文档的任何有效表达式。 |
示例
让我们通过以下示例 json 来了解用法。
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
"location": {
"lat": 60.1441,
"lon": -141.5012
},
"staff": {
"totalStaff": {
"fullTime": 2,
"partTime": 0
}
},
"sales": {
"salesByCategory": [
{
"categoryName": "DJ Headphones",
"totalSales": 35921
}
],
"fullSales": 3700
},
"promotionEvents": [
{
"eventName": "Bargain Blitz Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 3,
"Day": 11
},
"endDate": {
"Year": 2024,
"Month": 2,
"Day": 18
}
},
"discounts": [
{
"categoryName": "DJ Turntables",
"discountPercentage": 18
},
{
"categoryName": "DJ Mixers",
"discountPercentage": 15
}
]
}
],
"tag": [
"#ShopLocal",
"#SeasonalSale",
"#FreeShipping",
"#MembershipDeals"
]
}
如果要计算文档的 BSON 大小，请将其添加为名为 bsonSize 的新字段。
db.stores.aggregate([
{
$project: {
_id: 1,
name: 1,
documentSize: {
$bsonSize: "$$ROOT" //pass the whole document
}
}
},
// Limit the result to the first 3 documents
{ $limit: 3 }
])
此查询将返回以下文档。
[
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
"documentSize": 957
},
{
"_id": "649626c9-eda1-46c0-a27f-dcee19d97f41",
"name": "VanArsdel, Ltd. | Musical Instrument Outlet - East Cassie",
"documentSize": 1046
},
{
"_id": "8345de34-73ec-4a99-9cb6-a81f7b145c34",
"name": "Northwind Traders | Bed and Bath Place - West Oraland",
"documentSize": 5656
}
]