mongodb数据关联

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost: 27017/mongo-relation', { useNewUrlParser: true, useUnifiedTopology: true}, err => {if (err) {console.log('数据库连接失败');
    }
    console.log('数据库连接成功');
})

const categorySchema = new mongoose.Schema({
    name: {type: String}

}, {toJSON: { virtuals: true}
});

categorySchema.virtual('posts', {
    // 本地键
    localField: '_id',
    // 关联的模型
    ref: 'Post',
    // 外键
    foreignField: 'categories',
    // 输出多个
    justOne: false
});
const Category = mongoose.model('Category', categorySchema);

const postSchema = new mongoose.Schema({
    title: {type: String},
    body: {type: String},
    category: {
        type: mongoose.SchemaTypes.ObjectId,
        ref: 'Category'
    },
    categories: [{
        type: mongoose.SchemaTypes.ObjectId,
        ref: 'Category'
    }]
});

const Post = mongoose.model('Post', postSchema);



async function init() {// const cats = await Category.find().populate('categories');
    // console.log(cats);

    //     [//   { _id: 5ee0a7f22adf1624e8b9b64d, name: 'nodejs', __v: 0},
    //   {_id: 5ee0a7f22adf1624e8b9b64e, name: 'vue.js', __v: 0}
    // ]

    // 加上 lean() 
    // const cats = await Category.find().populate('posts').lean();
    // console.log(cats);
    // [
    //     {
    //       _id: 5ee0a7f22adf1624e8b9b64d,
    //       name: 'nodejs',
    //       __v: 0,
    //       posts: [[Object] ]
    //     },
    //     {
    //       _id: 5ee0a7f22adf1624e8b9b64e,
    //       name: 'vue.js',
    //       __v: 0,
    //       posts: [[Object], [Object] ]
    //     }
    //   ]

    // cats[0].posts 查找第 1 个分类内容
    // const cats = await Category.find().populate('posts').lean();
    // console.log(cats[0].posts);
    // [
    //     {
    //       _id: 5ee0a74dc6a921238454fa52,
    //       title: '第 2 篇文章',
    //       body: '内容 2',
    //       __v: 9,
    //       category: 5ee0a7f22adf1624e8b9b64d,
    //       categories: [5ee0a7f22adf1624e8b9b64d, 5ee0a7f22adf1624e8b9b64e]
    //     }
    //   ]


    // JSON.stringify
    const cats = await Category.find().populate('posts').lean();
    console.log(JSON.stringify(cats));

    // [{"_id":"5ee0a7f22adf1624e8b9b64d","name":"nodejs","__v":0,
    // "posts":[{"_id":"5ee0a74dc6a921238454fa52",
    // "title":"第 2 篇文章","body":"内容 2","__v":9,
    // "category":"5ee0a7f22adf1624e8b9b64d",
    // "categories":["5ee0a7f22adf1624e8b9b64d","5ee0a7f22adf1624e8b9b64e"]}]},
    // {"_id":"5ee0a7f22adf1624e8b9b64e","name":"vue.js","__v":0,"posts":[{"_id":"5ee0a74dc6a921238454fa51","title":"第 1 篇文章","body":"内容 1","__v":5,"category":"5ee0a7f22adf1624e8b9b64d","categories":["5ee0a7f22adf1624e8b9b64e"]},{"_id":"5ee0a74dc6a921238454fa52","title":"第 2 篇文章","body":"内容 2","__v":9,"category":"5ee0a7f22adf1624e8b9b64d","categories":["5ee0a7f22adf1624e8b9b64d","5ee0a7f22adf1624e8b9b64e"]}]}]

    // await Post.insertMany([{
    //     title: '第 1 篇文章',
    //     body: '内容 1'
    // }, {
    //     title: '第 2 篇文章',
    //     body: '内容 2'
    // }]);
    // await Category.insertMany([{
    //         name: 'nodejs'
    //     },
    //     {
    //         name: 'vue.js'
    //     }
    // ]);
    // const category = await Category.find();
    // console.log(category);
    // const cat1 = await Category.findOne({name: 'nodejs'});
    // const cat2 = await Category.findOne({name: 'vue.js'});

    // const post1 = await Post.findOne({title: '第 1 篇文章'});
    // const post2 = await Post.findOne({title: '第 2 篇文章'});
    // posts.category
    // console.log(cat1);

    // post1.categories = [cat2];
    // post2.categories = [cat1, cat2];
    // await post1.save();
    // await post2.save();

    // const post = await Post.find();
    // console.log(post);
    // console.log(post1, post2);

    // const post = await Post.find().populate('categories')
    // console.log(post[0], post[1]);
}

init()