通过使用嵌套数组的查找进行Mongoose分组

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
  name: String,
  orders: [
    {
      product: String,
      quantity: Number
    }
  ]
});

const User = mongoose.model('User', userSchema);

User.aggregate([
  {
    $unwind: '$orders'
  },
  {
    $group: {
      _id: '$orders.product',
      totalQuantity: { $sum: '$orders.quantity' }
    }
  },
  {
    $project: {
      _id: 0,
      product: '$_id',
      totalQuantity: 1
    }
  }
]).exec((err, result) => {
  if (err) {
    console.error(err);
  } else {
    console.log(result);
  }
});

User.aggregate([
  {
    $facet: {
      smallOrders: [
        { $unwind: { path: '$orders', preserveNullAndEmptyArrays: true } },
        { $match: { 'orders.quantity': { $lte: 10 } } },
        { $group: { _id: '$orders.product', totalQuantity: { $sum: '$orders.quantity' } } }
      ],
      largeOrders: [
        { $unwind: { path: '$orders', preserveNullAndEmptyArrays: true } },
        { $match: { 'orders.quantity': { $gt: 10 } } },
        { $group: { _id: '$orders.product', totalQuantity: { $sum: '$orders.quantity' } } }
      ]
    }
  },
  {
    $project: {
      result: { $concatArrays: ['$smallOrders', '$largeOrders'] }
    }
  }
]).exec((err, result) => {
  if (err) {
    console.error(err);
  } else {
    console.log(result);
  }
});