如何解决MongoNotConnectedError：执行操作前需连接客户端的问题

我在开发项目时，使用种子文件为数据库填充测试数据，运行Node.js文件时出现如下错误：

Database connected
D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\operations\execute_operation.js:24
            throw new error_1.MongoNotConnectedError('Client must be connected before running operations');
                  ^

MongoNotConnectedError: Client must be connected before running operations
    at executeOperationAsync (D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\operations\execute_operation.js:24:19)
    at D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\operations\execute_operation.js:12:45
    at maybeCallback (D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\utils.js:338:21)
    at executeOperation (D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\operations\execute_operation.js:12:38)
    at Collection.insertOne (D:\OUWork\Year 6\TM470\Project\node_modules\mongodb\lib\collection.js:148:57)
    at NativeCollection.<computed> [as insertOne] (D:\OUWork\Year 6\TM470\Project\node_modules\mongoose\lib\drivers\node-mongodb-native\collection.js:226:33)
    at Model.$__handleSave (D:\OUWork\Year 6\TM470\Project\node_modules\mongoose\lib\model.js:309:33)
    at Model.$__save (D:\OUWork\Year 6\TM470\Project\node_modules\mongoose\lib\model.js:388:8)
    at D:\OUWork\Year 6\TM470\Project\node_modules\kareem\index.js:387:18
    at D:\OUWork\Year 6\TM470\Project\node_modules\kareem\index.js:113:15 {
  [Symbol(errorLabels)]: Set(0) {}
}

种子文件的JavaScript代码如下：

const mongoose = require('mongoose');
const MusicProduct = require('../database_models/musicproduct');
const BookProduct = require('../database_models/bookproduct');

const musicAlbums = require('./musicseeds');
const bookNovels = require('./bookseeds');

// Connnect to MongoDB
mongoose.connect('mongodb://127.0.0.1/music-bookApp');
mongoose.set('strictQuery', false);

// Logic to check that the database is connected properly
mongoose.connection.on('error', console.error.bind(console, 'connection error:'));
mongoose.connection.once('open', () => {
    console.log('Database connected');
});

//Fill the Music products database with 20 random albums taken from the music seeds file
const musicSeedDB = async () => {
    await MusicProduct.deleteMany({});
    for (let i = 0; i < 20; i++) {
        const randomMusic20 = Math.floor(Math.random() * 20);
        //const musicStock = Math.floor(Math.random() * 10) + 1;
        const musicItem = new MusicProduct({
            artistName: musicAlbums[randomMusic20].artist,
            albumName: musicAlbums[randomMusic20].title,
            //musicStock
        })
        await musicItem.save();
    }
};

//Fill the Book products database with 20 random books taken from the music seeds file
const bookSeedDB = async () => {
    await BookProduct.deleteMany({});
    for (let i = 0; i < 20; i++) {
        const randomBook20 = Math.floor(Math.random() * 20);
        //const bookStock = Math.floor(Math.random() * 10) + 1;
        const bookItem = new BookProduct({
            bookAuthor: bookNovels[randomBook20].authors,
            bookName: bookNovels[randomBook20].title,
            //ookStock
        })
        await bookItem.save();
    }
};

// Close the connection to DB after finish seeding
musicSeedDB().then(() => {
    mongoose.connection.close();
});

bookSeedDB().then(() => {
    mongoose.connection.close();
});

运行后数据库已成功更新为种子数据，但需要消除该错误，解决方法如下：

错误原因 #

1. 连接时机不匹配：mongoose.connect()是异步操作，直接调用种子函数时，数据库可能还未完成连接，导致部分操作执行时连接未就绪。
2. 重复关闭连接：两个种子函数并行执行，其中一个完成后立即关闭连接，另一个函数此时仍在执行数据库操作，触发连接已关闭的错误。

修复后的代码 #

const mongoose = require('mongoose');
const MusicProduct = require('../database_models/musicproduct');
const BookProduct = require('../database_models/bookproduct');

const musicAlbums = require('./musicseeds');
const bookNovels = require('./bookseeds');

mongoose.set('strictQuery', false);

// 封装完整种子流程，确保连接就绪后再执行操作
const seedDatabase = async () => {
    try {
        // 等待数据库连接成功
        await mongoose.connect('mongodb://127.0.0.1/music-bookApp');
        console.log('Database connected');

        // 依次执行音乐和书籍的种子填充
        await musicSeedDB();
        await bookSeedDB();

        console.log('Seeding completed successfully');
    } catch (err) {
        console.error('Seeding failed:', err);
    } finally {
        // 所有操作完成后统一关闭连接
        await mongoose.connection.close();
        console.log('Database connection closed');
    }
};

const musicSeedDB = async () => {
    await MusicProduct.deleteMany({});
    for (let i = 0; i < 20; i++) {
        const randomMusic20 = Math.floor(Math.random() * 20);
        const musicItem = new MusicProduct({
            artistName: musicAlbums[randomMusic20].artist,
            albumName: musicAlbums[randomMusic20].title
        });
        await musicItem.save();
    }
};

const bookSeedDB = async () => {
    await BookProduct.deleteMany({});
    for (let i = 0; i < 20; i++) {
        const randomBook20 = Math.floor(Math.random() * 20);
        const bookItem = new BookProduct({
            bookAuthor: bookNovels[randomBook20].authors,
            bookName: bookNovels[randomBook20].title
        });
        await bookItem.save();
    }
};

// 启动种子流程
seedDatabase();

修复说明 #

• 使用await mongoose.connect()确保数据库连接完成后再执行后续操作，彻底避免连接未就绪的问题。
• 将两个种子函数放在同一异步流程中依次执行，避免并行操作导致的资源冲突。
• 用try/catch/finally统一处理错误和连接关闭，确保所有种子操作完成后才关闭数据库连接。
• 移除原有的mongoose.connection.once('open')监听，因为await mongoose.connect()已经会等待连接成功。

内容的提问来源于stack exchange，提问作者NewtoJavaHelp