在MongoDB和Express中获取产品评论的平均评分

// 引入所需的模块和库
const express = require('express');
const MongoClient = require('mongodb').MongoClient;

// 创建Express应用
const app = express();

// 定义MongoDB连接URL和数据库名称
const url = 'mongodb://localhost:27017';
const dbName = 'your_database_name';

// 创建获取产品评论的路由
const router = express.Router();
router.get('/products/:productId/reviews/average', (req, res) => {
  const productId = req.params.productId;

  // 连接到MongoDB数据库
  MongoClient.connect(url, (err, client) => {
    if (err) {
      console.error('Failed to connect to MongoDB:', err);
      res.status(500).send('Failed to connect to MongoDB');
      return;
    }

    // 获取数据库和集合对象
    const db = client.db(dbName);
    const collection = db.collection('products');

    // 使用聚合管道计算平均评分
    collection.aggregate([
      { $match: { _id: productId } },
      { $unwind: '$reviews' },
      {
        $group: {
          _id: '$_id',
          averageRating: { $avg: '$reviews.rating' }
        }
      }
    ]).toArray((err, result) => {
      if (err) {
        console.error('Failed to fetch average rating:', err);
        res.status(500).send('Failed to fetch average rating');
        return;
      }

      // 返回计算得到的平均评分
      if (result.length > 0) {
        res.json({ averageRating: result[0].averageRating });
      } else {
        res.json({ averageRating: 0 });
      }

      // 关闭数据库连接
      client.close();
    });
  });
});

// 将路由挂载到Express应用
app.use('/api', router);

// 启动Express应用
app.listen(3000, () => {
  console.log('Server is running on port 3000');
});