4.typeorm 多对一查询

多对一查询

一对多反过来就是多对一，所以多对一的实体类配置和一对多的实体类配置是相同的，只是他们的差异存在于调用的查询的 **Respository ** 是那个类型的 Respository，一家查询的时候配置的 relations 是那个关联对象的属性

User 实体类

import { Column, Entity, JoinColumn, JoinTable, 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[];
}

Article 实体类

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;
}

Article 服务

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

@Injectable()
export class ArticleService {
  @InjectRepository(Article)
  private readonly articleRespository: Repository<Article>;
  
  // 多对一查询
  getUserOfarticle () {
    return this.articleRespository.find({
      relations: ['user']
    })
  }
}

查询结果

[
    {
        "id": "0fcb8310-9c4a-11ea-9427-017d0539b705",
        "title": "fe'f",
        "link": null,
        "fileId": null,
        "content": "<p>微任务</p>",
        "categoryId": "4b958080-9a33-11ea-9abc-1d8c64f552b3",
        "formatId": 2,
        "originId": 1,
        "createBy": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
        "user": {
            "id": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
            "nickname": "李云龙",
            "username": "wanghailong",
            "password": "1bbd886460827015e5d605ed44252251",
            "avator": "http://192.168.1.101:8765/avator/f360e610-9d80-11ea-9008-019523360f5b.jpg",
            "email": "5r236g33@test.com"
        }
    }
]

生成的SQL语句分析

SELECT
	`Article`.`id` AS `Article_id`,
	`Article`.`title` AS `Article_title`,
	`Article`.`link` AS `Article_link`,
	`Article`.`fileId` AS `Article_fileId`,
	`Article`.`content` AS `Article_content`,
	`Article`.`categoryId` AS `Article_categoryId`,
	`Article`.`formatId` AS `Article_formatId`,
	`Article`.`originId` AS `Article_originId`,
	`Article`.`createBy` AS `Article_createBy`,
	`Article__user`.`id` AS `Article__user_id`,
	`Article__user`.`nickname` AS `Article__user_nickname`,
	`Article__user`.`username` AS `Article__user_username`,
	`Article__user`.`password` AS `Article__user_password`,
	`Article__user`.`avator` AS `Article__user_avator`,
	`Article__user`.`email` AS `Article__user_email` 
FROM
	`article` `Article`
	LEFT JOIN `user` `Article__user` ON `Article__user`.`id` = `Article`.`createBy`

通过上面的 sql 语句可以看出，typeorm 查询的时候是以 Article 表为主表，关联 User 表进行查询，对着返回结果 typeorm 再进行分类处理，最终形成我们看到的 json 对象