Node.js MongoDB 限制
限制结果
在 MongoDB 中，我们可以使用 limit() 方法来限制结果。
limit() 方法接受一个参数，一个数字，表示要返回的文档数量。
假设你有一个名为“customers”的集合
customers
[
{ _id: 58fdbf5c0ef8a50b4cdd9a84 , name: 'John', address: 'Highway 71'},
{ _id: 58fdbf5c0ef8a50b4cdd9a85 , name: 'Peter', address: 'Lowstreet 4'},
{ _id: 58fdbf5c0ef8a50b4cdd9a86 , name: 'Amy', address: 'Apple st 652'},
{ _id: 58fdbf5c0ef8a50b4cdd9a87 , name: 'Hannah', address: 'Mountain 21'},
{ _id: 58fdbf5c0ef8a50b4cdd9a88 , name: 'Michael', address: 'Valley 345'},
{ _id: 58fdbf5c0ef8a50b4cdd9a89 , name: 'Sandy', address: 'Ocean blvd 2'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8a , name: 'Betty', address: 'Green Grass 1'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8b , name: 'Richard', address: 'Sky st 331'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8c , name: 'Susan', address: 'One way 98'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8d , name: 'Vicky', address: 'Yellow Garden 2'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8e , name: 'Ben', address: 'Park Lane 38'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8f , name: 'William', address: 'Central st 954'},
{ _id: 58fdbf5c0ef8a50b4cdd9a90 , name: 'Chuck', address: 'Main Road 989'},
{ _id: 58fdbf5c0ef8a50b4cdd9a91 , name: 'Viola', address: 'Sideway 1633'}
]
示例
限制结果只返回 5 个文档
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://127.0.0.1:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("mydb");
dbo.collection("customers").find().limit(5).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});
运行示例 »
将上面的代码保存到名为“demo_mongodb_limit.js”的文件中，然后运行该文件。
运行 "demo_mongodb_limit.js"
C:\Users\Your Name>node demo_mongodb_limit.js
结果如下：
customers
[
{ _id: 58fdbf5c0ef8a50b4cdd9a84 , name: 'John', address: 'Highway 71'},
{ _id: 58fdbf5c0ef8a50b4cdd9a85 , name: 'Peter', address: 'Lowstreet 4'},
{ _id: 58fdbf5c0ef8a50b4cdd9a86 , name: 'Amy', address: 'Apple st 652'},
{ _id: 58fdbf5c0ef8a50b4cdd9a87 , name: 'Hannah', address: 'Mountain 21'},
{ _id: 58fdbf5c0ef8a50b4cdd9a88 , name: 'Michael', address: 'Valley 345'}
]
如上结果所示，只返回了前 5 个文档。
