Nestjs如何将两个表与中间的表正确映射

Question

我使用Postgres作为数据库，下面有表：

学生

id: Integer (PK)
name: Text

主题

id: Integer (PK)
name: Text

学生分配

student_id: Integer (PK)
subject_id: Integer (PK)

那些表没有Auto-generated PK。所以，我的实体是：

学生实体.ts

import { Entity, Column, PrimaryGeneratedColumn, OneToMany, PrimaryColumn } from 'typeorm';
import { student_assignation } from './student_assignation.entity';
import { Subject } from './subject.entity';
@Entity()
export class Student {
@Column('number')
@PrimaryColumn()
id: number;
@Column('text')
name: string;
@OneToMany(type => student_assignation, x => x.subject_id)
//student_assignations: student_assignation[];
}

好吧，这是我的问题：我正在尝试将所有主题分配给一个用户。在SQL术语中，我将其定义为：

SELECT 
u.id, u.name, r.id, r.name
FROM  
student u INNER JOIN student_assignation ra
ON u.id = ra.student_id
INNER JOIN subject r
ON r.id = ra.subject_id
WHERE
u.id = 1

但目前要在nestjs中转换和使用它，我有这样的关系：

@OneToMany(type => student_assignation, x => x.subject_id)
@ManyToOne(type => subject, x => x.id)

但是，没有检索到任何信息。

Answer 1

您需要多对多关系。看看这里的TypeOrm实现

Answer 2

您必须在many-to-many关系中实现您的实体：

@Entity()
export class Student {
@Column('number')
@PrimaryColumn()
id: number;
@Column('text')
name: string;
@ManyToMany(type => Subject)
@JoinTable({ name: 'student_assignation' })
subjects: Subject[];
}

@Entity()
export class Subject {
@PrimaryColumn()
id: number;
@Column()
name: string;
@ManyToMany(type => Student)
students: Student[];
}

检索具有所有主题的用户：

const user = await User.findOne(USER_ID, { relations: ['subjects'] })
console.log(user.subjects);