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
该错误令我感到困惑,因为我对newFunction使用了“异步”。我尝试过更改“异步”和“等待”的位置,但是到目前为止,我没有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}`);
您的代码有重大更改,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));
开发人员常常会对async/await
&的用法感到困惑,他们确实将async / await与callback()混合在一起。因此,请检查以下问题或代码中不需要的部分:
SyntaxError:await仅在异步函数中有效-是因为您不能
await
在之外使用async function
。
在这一行dbo.collection("users").find({}).toArray(function (err, result) {
-async
由于await
必须在其中使用它,因此必须具有功能。
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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