一對多查詢

一對多關系描述

1. 一對多關系允許在 Entity1 可以擁有 Entity2 的多個實例時創(chuàng)建關系類型舀寓。
2. Entity2 只有一個 Entity1胆数。Entity2 是關系的所有者，并在其自身存儲 Entity1 主鍵列的值互墓。
3. 兩張表之間存在一對多關系必尼，那么反之就是多對一的關系

相關注解說明

1. @OneToMany 注解

   // 源碼內容
   export declare function OneToMany<T>(typeFunctionOrTarget: string | ((type?: any) => ObjectType<T>), inverseSide: string | ((object: T) => any), options?: RelationOptions): PropertyDecorator;
   改在
   

   接收三個參數：

   ? typeFunctionOrTarget：關聯(lián)查詢的目標類型，即副表類篡撵，字符串類型或者一個返回目標類型的函數判莉，必填

   ? inverseSide: 副表實體類中關聯(lián)主表的實體類屬性，字符串類型或者一個返回目標類型的函數

   ? options：用于配置關聯(lián)關系

2. @ManyToOne 注解

   參數同上育谬，主要說明如下：

   這里的 typeFunctionOrTarget 就是 One 所指的實體類券盅，相應的就是主表類

   inverseSide 就是主表實體類上定義的副表(即當前表)的屬性，也是函數

3. @JoinColumn 注解

   用于標注在一對一或者多對一的關系中配置關聯(lián)關系膛檀，參數格式

   export interface JoinColumnOptions {
       // 主表中的主鍵列所對應的該表中的關聯(lián)的列的列名稱
       name?: string;
       // 引用此列的實體中的列的名稱
       referencedColumnName?: string;
   }
   
   

User 實體類

import { Column, Entity, OneToMany, PrimaryColumn } from "typeorm";
import { Article } from "./article.entity";

@Entity('user')
export class User {
  @PrimaryColumn()
  id: string;

  @Column()
  nickname: string;

  @Column()
  username: string;

  @Column()
  password: string;

  @Column()
  avator: string;

  @Column()
  email: string;

  @OneToMany((type) => Article, (article) => article.user)
  articles: Article[];
}

備注：一對多的關系中锰镀，需要給主表的實體類設置一個副表關聯(lián)的實體類屬性娘侍，并通過 @OneToMany 進行注解，

Article 實體類

import { Column, Entity, JoinColumn, ManyToOne, PrimaryColumn } from "typeorm";
import { User } from "./user.entity";

@Entity('article')
export class Article {
  @PrimaryColumn()
  id: string;

  @Column()
  title: string;

  @Column()
  link: string;

  @Column()
  fileId: string;

  @Column('text')
  content: string;

  @Column()
  categoryId: string;

  @Column()
  formatId: number;

  @Column()
  originId: number;

  @Column()
  createBy: string;

  @ManyToOne((type) => User, (user) => user.articles)
  @JoinColumn({ name: 'createBy' })
  user: User;
}

鏈接關系

User.id === Article.createBy

服務

import { Injectable } from "@nestjs/common";
import { InjectRepository } from "@nestjs/typeorm";
import { Article } from "../../entities/article.entity";
import { Attachment } from "../../entities/attachment.entity";
import { Repository } from "typeorm";
import { User } from "../../entities/user.entity";

@Injectable()
export class UserService {
  constructor(@InjectRepository(User) private readonly userRepository: Repository<User>){}

  // 一對多查詢
  getUserOfArticle () {
    return this.userRepository.find({
      relations: ['articles']
    })
  }
}

查詢結果

[
    {
        "id": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
        "nickname": "李云龍",
        "username": "wanghailong",
        "password": "1bbd886460827015e5d605ed44252251",
        "avator": "http://192.168.1.101:8765/avator/f360e610-9d80-11ea-9008-019523360f5b.jpg",
        "email": "59652111558733@qq.com",
        "articles": [
            {
                "id": "0fcb8310-9c4a-11ea-9427-017d0539b705",
                "title": "fe'f",
                "link": null,
                "fileId": null,
                "content": "<p>微任務</p>",
                "categoryId": "4b958080-9a33-11ea-9abc-1d8c64f552b3",
                "formatId": 2,
                "originId": 1,
                "createBy": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464"
            },
             {
                "id": "11dbc240-9c46-11ea-9427-017d0539b705",
                "title": "antd design",
                "link": "https://www.antdv.com/components/form-cn/",
                "fileId": null,
                "content": null,
                "categoryId": "b8504210-99fb-11ea-ac42-a10a286651a2",
                "formatId": 3,
                "originId": 3,
                "createBy": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464"
            }
        ]
    }
]