javascript - 如何通过 promise 在mongodb中关闭连接？

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How do I access previous promise results in a .then() chain?
                                
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我想在NodeJS中为MongoDB使用Promise。因此，我有一些代码：

const mongo = require('mongodb').MongoClient;
const config = require('./config.json');

mongo.connect(config.URI, function (err, client) {
  const db = client.db("INDFLORIST");
  const collection = db.collection('API');
  collection.insertOne({name: 'Roger'}, function (err, res) {
    if (err) throw err;
    console.log("Document inserted");
    client.close();
  });
});

然后将callback转换为promise：

const mongo = require('mongodb').MongoClient;
const config = require('./config.json');

mongo.connect(config.URI).then(client => {
    const db = client.db("INDFLORIST");
    const collection = db.collection('API');
    return collection.insertOne({name: 'Roger'});
})
.then(function(result) {
    console.log("Document inserted");
}).then(client => {
    client.close();
})
.catch(err => {
    console.error(err);
});

但是此脚本调用错误：TypeError：无法读取未定义的属性“ close”。

你能帮我吗？如何解决这个问题？

最佳答案

您可以创建一些外部变量_client_，并在成功连接后为它分配client，然后可以使用_client_在上一个then回调中关闭连接。

const mongo = require("mongodb").MongoClient;
const config = require("./config.json");
let _client_; // <-- external variable
mongo.connect(config.URI).then(client => {
    _client_ = client; // <-- assing real client to it
    const db = client.db("INDFLORIST");
    const collection = db.collection("API");
    return collection.insertOne({name: "Roger"});
}).then(function (result) {
    console.log("Document inserted");
}).then(() => {
    _client_.close(); // <-- close connection
}).catch(err => {
    console.error(err);
});

您还可以通过所有then回调传递它

const mongo = require("mongodb").MongoClient;
const config = require("./config.json");
mongo.connect(config.URI).then(client => {
    const db = client.db("INDFLORIST");
    const collection = db.collection("API");
    return collection.insertOne({name: "Roger"}).then(() => client);
}).then(function (client) {
    console.log("Document inserted");
    return client;
}).then(client => {
    client.close();
}).catch(err => {
    console.error(err);
});