mongoose组通过查找字段

我是NodeJS和Mongoose的新手，我试图做一些高级查询。

我有三个文件（类别，子类别和产品）

Category.js

var mongoose = require('mongoose'); var CategorySchema = new mongoose.Schema({ name: { type: String, required: true } }); mongoose.model('Category', CategorySchema); module.exports = mongoose.model('Category'); 

Subcategory.js

 var mongoose = require('mongoose'); var SubcategorySchema = new mongoose.Schema({ name: { type: String, required: true }, image: { type: Buffer, contentType: String }, idcategory: { type: mongoose.Schema.Types.ObjectId, ref: 'Category' } }); mongoose.model('Subcategory', SubcategorySchema); module.exports = mongoose.model('Subcategory'); 

Product.js

 var mongoose = require('mongoose'); var ProductSchema = new mongoose.Schema({ name: { type: String, required: true }, idsubcategory: { type: mongoose.Schema.Types.ObjectId, ref: 'Subcategory', required: true }, price: { type: Number, required: true } }); mongoose.model('Product', ProductSchema); module.exports = mongoose.model('Product'); 

所以，一个产品有一个具有类别的子类别。 由于我有这个结构，我想按类别来计数我的产品。 IG

 [ { "categoryName": "cat1": quantity: 10 }, { "categoryName": "cat2": quantity: 5 }, { "categoryName": "cat3": quantity: 2 } ] 

我已经尝试$ $查找与$组没有成功，因为我不明白的聚合。

mongoose：“4.11.6”

Answer 1

尝试这个

 CategoryModel.aggregate([ // stage 1: join subcategories { $lookup: { from: 'subcategories', // collection to join localField: '_id', // field from categories collection foreignField: 'idcategory', // field from subcategories collection as: 'subcategory' } }, // at this point, each document will have an additional subcategory array with all the "joined" documents from subcategories collection // stage 2: we need to "unwind" the subcategory array in order to join the products // when you unwind an array, it's like making each element in the array have its own document { $unwind: '$subcategory' }, // stage 3: join products { $lookup: { from: 'products', // collection to join localField: 'subcategory._id', // field from our updated collection foreignField: 'idsubcategory', // field from products collection as: 'products' } }, // EDIT // stage 4: strip out all fields except _id, category name, and quantity (number of products) { $project: { name: true, quantity: { $size: '$products' } } }, // stage 5: group by category ID { $group: { _id: '$_id', // group by category ID categoryName: { $first: '$name' }, // get category name quantity: { $sum: '$quantity' }, // sum the quantities } } ]).exec(...);