关联查询

Article 实体类

// 文件位置: /src/entities/article.entity.ts
import { Column, Entity, PrimaryColumn } from "typeorm";

@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;
}

User 实体类

// 文件位置: /src/entities/user.entity.ts
import { Column, Entity, PrimaryColumn } from "typeorm";

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

  @Column()
  nickname: string;

  @Column()
  username: string;

  @Column()
  password: string;

  @Column()
  avator: string;

  @Column()
  email: string;
}

表关联关系: article.createBy === user.id

ArticleService 服务代码

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>;

  getAllUsers () {
    return this.articleRespository.createQueryBuilder()
      .leftJoinAndSelect(User, 'user', 'user.id = article.createBy')
      // .select(`
      //   article.id as id,
      //   article.title as title,
      //   article.content as content,
      //   user.id as userId,
      //   user.nickname as nickname,
      //   user.username as usernmae,
      //   user.avator as avator
      // `)
      .getRawMany();
  }
}
// 对应生成的sql:
/*
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`,
    `user`.`id` AS `user_id`,
    `user`.`nickname` AS `user_nickname`,
    `user`.`username` AS `user_username`,
    `user`.`password` AS `user_password`,
    `user`.`avator` AS `user_avator`,
    `user`.`email` AS `user_email` 
FROM
    `article` `Article`
    LEFT JOIN `user` `user` ON `user`.`id` = article.createBy
*/
// 返回结果:
[
    {
        "Article_id": "0fcb8310-9c4a-11ea-9427-017d0539b705",
        "Article_title": "fe'f",
        "Article_link": null,
        "Article_fileId": null,
        "Article_content": "<p>微任务</p>",
        "Article_categoryId": "4b958080-9a33-11ea-9abc-1d8c64f552b3",
        "Article_formatId": 2,
        "Article_originId": 1,
        "Article_createBy": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
        "user_id": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
        "user_nickname": "李云龙",
        "user_username": "wanghailong",
        "user_password": "1bbd886460827015e5d605ed44252251",
        "user_avator": "http://192.168.1.101:8765/avator/f360e610-9d80-11ea-9008-019523360f5b.jpg",
        "user_email": "5xx1xx733@test.com"
    }
]

// 放开上面注掉的 "select" 代码

// 对应生成的sql:
/*
SELECT
        article.id as id,
        article.title as title,
        article.content as content,
        `user`.`id` as userId,
        `user`.`nickname` as nickname,
        `user`.`username` as usernmae,
        `user`.`avator` as avator
       FROM `article` `Article` LEFT JOIN `user` `user` ON `user`.`id` = article.createBy
*/
// 进行查询，可以得出如下的查询结果:
[
    {
        "id": "0fcb8310-9c4a-11ea-9427-017d0539b705",
        "title": "fe'f",
        "content": "<p>微任务</p>",
        "userId": "16ffe4f0-98d0-11ea-adcb-cd4aa44d4464",
        "nickname": "李云龙",
        "usernmae": "wanghailong",
        "avator": "http://192.168.1.101:8765/avator/f360e610-9d80-11ea-9008-019523360f5b.jpg"
    }
]

结论:

1. typeorm 有一套默认生成查询列的方式，其生成出来的查询列的格式是："表名_列名"
2. typeorm 生成的列是根据实体类中定义的字段进行生成的，也就是实体类中有多少个字段就生成多少个查询列
3. 默认的生成列的方式可以通过 .select() 方法进行重置，并且同时根据自定义的查询列只返回我们想要的列，同时还能重命名列

相关方法说明

1. createQueryBuilder() 方法的调用可以传递一个实体类名称，如果是通过 Respository 的子类调用的，那么就可以不传递实体类名称
2. leftJoinAndSelect() 方法有多个重载方法，第一个参数可以是一个实体类名称，还可以是一个实体类型
3. getRawMany() 方法根据生成器的生成的 sql 进行查询并返回查询结果