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[英]Node Js - SyntaxError: await is only valid in async function
[英]SyntaxError: await is only valid in async function, When connecting to Mongo DB using Node JS
我正在尝试使用下面提供的代码在 Javascript 中使用 async/await 函数访问 mongo 数据库。 当我运行代码时,终端返回以下错误:
SyntaxError: await is only valid in async function
这个错误让我很困惑,因为我对 newFunction 使用了“异步”。 我曾尝试更改“async”和“await”的位置,但迄今为止我尝试过的任何组合都无法成功执行。 任何见解将不胜感激。
var theNames;
var url = 'mongodb://localhost:27017/node-demo';
const newFunction = async () => {
MongoClient.connect(url, function (err, db) {
if (err) throw err;
var dbo = db.db("node-demo");
//Find the first document in the customers collection:
dbo.collection("users").find({}).toArray(function (err, result) {
if (err) throw err;
theNames = await result;
return theNames;
db.close();
});
});
}
newFunction();
console.log(`Here is a list of theNames: ${theNames}`);
错误是正确的,因为该函数不是异步函数。 在toArray
async
回调函数。
例子
var theNames;
var url = 'mongodb://localhost:27017/node-demo';
const newFunction = async () => {
MongoClient.connect(url, function (err, db) {
if (err) throw err;
var dbo = db.db("node-demo");
//Find the first document in the customers collection:
dbo.collection("users").find({}).toArray( async function (err, result) {
if (err) throw err;
theNames = await result;
return theNames;
db.close();
});
});
}
newFunction();
console.log(`Here is a list of theNames: ${theNames}`);
您的代码有重大变化,请尝试以下操作:
对于猫鼬:
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
let theNames;
let url = 'mongodb://localhost:27017/node-demo';
const usersSchema = new Schema({
any: {}
}, {
strict: false
});
const Users = mongoose.model('users', usersSchema, 'users');
const newFunction = async () => {
let db = null;
try {
/** In real-time you'll split DB connection(into another file) away from DB calls */
await mongoose.connect(url, { useNewUrlParser: true });
db = mongoose.connection;
let dbResp = await Users.find({}).limit(1).lean() // Gets one document out of users collection. Using .lean() to convert MongoDB documents to raw Js objects for accessing further.
// let dbResp = await Users.find({}).lean(); - Will get all documents.
db.close();
return dbResp;
} catch (err) {
(db) && db.close();
console.log('Error at newFunction ::', err)
throw err;
}
}
newFunction().then(res => console.log('Printing at calling ::', res)).catch(err => console.log('Err at Calling ::', err));
对于 MongoDB 驱动程序:
const MongoClient = require('mongodb').MongoClient;
const newFunction = async function () {
// Connection URL
const url = 'mongodb://localhost:27017/node-demo';
let client;
try {
// Use connect method to connect to the Server
client = await MongoClient.connect(url);
const db = client.db(); // MongoDB would return client and you need to call DB on it.
let dbResp = await db.collection('users').find({}).toArray(); // As .find() would return a cursor you need to iterate over it to get an array of documents.
// let dbResp = await db.collection('users').find({}).limit(1).toArray(); - For one document
client.close();
return dbResp;
} catch (err) {
(client) && client.close();
console.log(err);
throw err
}
};
newFunction().then(res => console.log('Printing at calling ::', res)).catch(err => console.log('Err at Calling ::', err));
开发人员经常对async/await
的使用感到困惑,他们将 async/await 与 callback() 混淆。 因此,请检查以下代码中的问题或不需要的部分:
语法错误:AWAIT仅在异步功能有效-是因为你不能使用
await
的外部async function
。
在这一行dbo.collection("users").find({}).toArray(function (err, result) {
- 它必须是async
函数,因为await
其中使用了await
。
var theNames; // There is nothing wrong using var but you can start using let.
var url = 'mongodb://localhost:27017/node-demo';
const newFunction = async () => {
MongoClient.connect(url, function (err, db) {
if (err) throw err;
var dbo = db.db("node-demo"); // You don't need it as you're directly connecting to database named `node-demo` from your db url.
//Find the first document in the customers collection:
/** If you create a DB connection with mongoose you need to create schemas in order to make operations on DB.
Below syntax goes for Node.Js MongoDB driver. And you've a mix n match of async/await & callbacks. */
dbo.collection("users").find({}).toArray(function (err, result) { // Missing async keyword here is throwing error.
if (err) throw err;
theNames = await result;
return theNames;
db.close(); // close DB connection & then return from function
});
});
}
newFunction();
console.log(`Here is a list of theNames: ${theNames}`);
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