使用Mongoose populateImplement multi-table association and query

mongodb不是传统的关系型数据库,我们可以使用monogooseIt is convenient to associate multiple tables,实现一对多、Many-to-many data table storage and query functions.
This article has the most common one-to-many relationship model,Introduce a simple data model definition、存储、查询.

一、 数据模型创建

我们创建一个Person模型和一个Story模型,其中一个Person对应多个Story,This is a typical one-to-many relationship.

1. 创建一个PersonSchema

创建PersonSchema时,It does not need to be specified for it_id属性,Because the database automatically adds a primary key attribute to it.
由于一个PersonObjects can have more than oneStory对象,所以需要添加一个stories数组属性,store associated with itStory.
具体代码如下：

const PersonSchema = new Schema({
    
    // _id: Schema.Types.ObjectId, 
    name: String,
    age: Number,
    stories: [{
     type: Schema.Types.ObjectId, ref: 'Story' }]
})

问题解答
其中的Schema.Types.ObjectIdis a built-in special type,Specially used to represent objectsID
官方解读：An ObjectId is a special type typically used for unique identifiers.

2. 创建一个StorySchema

每个Story都有一个唯一的author,也就是一个Person对象.Unlike ordinary properties,We need to specify the type of the referenced property and the referenced model name.同样的,每个StoryObjects can also have more than onefans,同样是Person对象.There is actually a circular reference here.
Students who have studied relational databases,Probably very easy to understand here.

const StorySchema = new Schema({
    
    author: {
     type: Schema.Types.ObjectId, ref: 'Person' },
    title: String,
    fans: [{
     type: Schema.Types.ObjectId, ref: 'Person' }]
})

3. 使用Schema创建对应的model

Need to use to create a modelmongoose.model方法,该方法可以接收三个参数,其中：

1. The first parameter refers to the name of the model
2. The second parameter refers to the usedSchema
3. The third parameter refers to the correspondingmongodb数据表（集合）
   The following codes are used respectivelyStorySchema和PersonSchema创建了一个Story模型和一个Person模型

const Story = mongoose.model('Story', StorySchema, 'tb_story')
const Person = mongoose.model('Person', PersonSchema, 'tb_person')

二、数据存储

使用mongooseData access can be done very simply in an object-oriented way.

1. 创建模型实例

创建一个名为xiaoming的Person对象,然后再创建一个Story,and make it referencePerson._id属性.

let p1 = new Person({
    
    name: 'xiaoming',
    age: 12
})
let s1 = new Story({
    
    title: 'The life of snow white and the dwarfs',
    author: p1._id
})
s1.fans.push(p1.id)

问题解读
There's an outlier here,That's why I made the writer of the story a fan of the story here~~

2. Store model data

使用模型的.save()The method stores the object's data in the database.

p1.save().then(person => {
    
    console.log('Pserson save success.\n', person)
    s1.save().then(story => {
    
        console.log('Story save success.\n', story)
    })
})

代码指向结果如下：

Pserson save success.
 {
    
  name: 'xiaoming',
  age: 12,
  stories: [],
  _id: new ObjectId("62ef6fb11c8795f4e1327adb"),	  //注意,This corresponds to the followingStory.author
  __v: 0
}
Story save success.
 {
    
  author: new ObjectId("62ef6fb11c8795f4e1327adb"),   //注意,这里对应了上面的Person._id
  title: 'The life of snow white and the dwarfs',
  fans: [ new ObjectId("62ef6fb11c8795f4e1327adb") ],
  _id: new ObjectId("62ef6fb11c8795f4e1327adc"),
  __v: 0
}

This completes the data storage job.

三、数据关联查询

1. Use the title of the story,Look up the name of the author of the story

Story.findOne({
     title: 'The life of snow white and the dwarfs' })
    .populate('author').then(story => {
    
        console.log(story.author.name)
    })

执行结果会输出：xiaoming
2. Use a story title,Inquire about fan information

Story.findOne({
     title: 'The life of snow white and the dwarfs' })
	.populate('fans').then(story => {
    
    	console.log(story.fans)
	})

代码执行结果：

[
	 {
    
	  name: 'xiaoming',
	  age: 12,
	  stories: [],
	  _id: new ObjectId("62ef781a8123a8ec47f40736"),
	  __v: 0
	}
]

四、完整代码

const mongoose = require('mongoose')
const Schema = mongoose.Schema

mongoose.connect('mongodb://ahohAdmin:[email protected]:27017/db_ahoh')
    .then('database connected')
    .catch(err => console.log(err))

const PersonSchema = new Schema({
    
    // _id: Schema.Types.ObjectId,
    name: String,
    age: Number,
    stories: [{
     type: Schema.Types.ObjectId, ref: 'Story' }]
})

const StorySchema = new Schema({
    
    author: {
     type: Schema.Types.ObjectId, ref: 'Person' },
    title: String,
    fans: [{
     type: Schema.Types.ObjectId, ref: 'Person' }]
})

const Story = mongoose.model('Story', StorySchema, 'tb_story')
const Person = mongoose.model('Person', PersonSchema, 'tb_person')


let p1 = new Person({
    
    name: 'xiaoming',
    age: 12
})
let s1 = new Story({
    
    title: 'The life of snow white and the dwarfs',
    author: p1._id
})
s1.fans.push(p1.id)
p1.save().then(person => {
    
    console.log('Pserson save success.\n', person)
    s1.save().then(story => {
    
        console.log('Story save success.\n', story)

    })
})

Story.findOne({
     title: 'The life of snow white and the dwarfs' })
    .populate('author').then(story => {
    
        console.log(story.author.name)
    })

Story.findOne({
     title: 'The life of snow white and the dwarfs' }).populate('fans').then(story => {
    
    console.log(story.fans)
})