如何获取mongoose中所有集合中两个字段乘积的总和

const mongoose = require('mongoose');

// 连接到MongoDB数据库
mongoose.connect('mongodb://localhost/mydatabase', { useNewUrlParser: true, useUnifiedTopology: true });

// 定义数据模型
const MyModel = mongoose.model('MyModel', new mongoose.Schema({
  field1: Number,
  field2: Number
}));

// 使用聚合管道获取两个字段乘积的总和
MyModel.aggregate([
  {
    $project: {
      product: { $multiply: ['$field1', '$field2'] }
    }
  },
  {
    $group: {
      _id: null,
      total: { $sum: '$product' }
    }
  }
])
  .then(result => {
    console.log(result);
    // 输出结果示例：[ { _id: null, total: 12345 } ]
  })
  .catch(error => {
    console.error(error);
  });