Node.js MongoDB Limit

限制结果

为了限制 MongoDB 中的结果，我们使用 limit() 方法。limit() 方法接受一个参数，一个定义要返回多少文档的数字。

假设你有一个 "customers" 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'}
]

实例

将结果限制为仅返回 5 个文档:

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
 if (err) throw err;
  var dbo = db.db("mydb");
  dbo.collection("customers").find()<strong>.limit(5)</strong>.toArray(function(err, result) {
   if (err) throw err;
  console.log(result);
   db.close();
 });
});

将上述代码保存在名为 "demo_mongodb_limit.js" 的文件中，然后运行该文件:

运行 "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'}
]

从上面的结果可以看出，只返回了前 5 个文档。