如何使用 TypeORM 将项目添加到多对多关联表答案

【问题标题】：How can I add item to many-to-many relationed table with TypeORM如何使用 TypeORM 将项目添加到多对多关联表
【发布时间】：2022-02-21 22:03:43
【问题描述】：

我需要有关 typeorm、typegraphql 的多对多问题的帮助。我尝试了很多方法将项目添加到 M-T-M 关系表中，但无法做到。我遵循了 TypeORM 文档，但我认为我遗漏了一些东西。

当我尝试从学院获取教师时，它返回未定义。应该是什么类型的？我认为它是一个数组，我可以轻松地将一个项目推送到它，或者传播旧值并添加一个项目。但是，上述方法都不起作用。

 @ObjectType()
@Entity()
export class Faculty extends BaseEntity {
  @Field(() => ID)
  @PrimaryColumn()
  id: string;

  @Field(() => [Department])
  @OneToMany(() => Department, (department) => department.faculty)
  departments: Department[];

  @Field(() => [Teacher], { nullable: true })
  @ManyToMany(() => Teacher)
  @JoinTable()
  teachers: Teacher[];

  @BeforeInsert()
  setId() {
    this.id = uuid();
  }
}



@ObjectType()
@Entity()
export class Teacher extends BaseEntity {
  @Field(() => ID)
  @PrimaryColumn()
  id: string;

  @Field(() => [Faculty])
  @ManyToMany(() => Faculty, (faculty) => faculty.teachers)
  faculties: Faculty[];

  @BeforeInsert()
  setId() {
    this.id = uuid();
  }
}



 @Mutation(() => Teacher)
  async addTeacherToFaculty(
    @Arg('teacherId') teacher_id: string,
    @Arg('facultyId') faculty_id: string
  ): Promise<Teacher> {
    const teacher = await Teacher.findOne({ where: { id: teacher_id } });

    let faculty = await Faculty.findOne({ where: { id: faculty_id } });

    if (!teacher) {
      throw new Error('Invalid credentials, please provide correct teacher ID');
    }

    if (!faculty) {
      throw new Error('Invalid credentials, please provide correct faculty ID');
    }

    const { teachers } = faculty;

    if (teachers && teachers.length == 0) {
      faculty.teachers = [teacher];
    } else {
      faculty.teachers?.push(teacher);
    }

    console.log(faculty.teachers);

    await faculty.save();

    return teacher;
  }

【问题讨论】：

标签： typescript typeorm typegraphql

【解决方案1】：

管理多对多关系的最简单方法是创建自己的自定义连接表。因此，Teacher 将与自定义连接表（让我们称之为连接表 TeacherFaculty）具有一对多的关系，并且 Faculty 也将与 TeacherFaculty 具有一对多的关系。 TeacherFaculty 将反过来与 Teacher 和 Faculty 建立多对一的关系。然后，您可以为它们的 id 定义列，这些列将被引用为它们的连接列。例如

@ObjectType()
@Entity()
export class Faculty extends BaseEntity {
  @Field(() => ID)
  @PrimaryColumn()
  id: string;

  @Field(() => [Department])
  @OneToMany(() => Department, (department) => department.faculty)
  departments: Department[];

  @OneToMany(() => TeacherFaculty, (tf) => tf.faculty)
  teacherConn: Promise<TeacherFaculty[]>;

  @BeforeInsert()
  setId() {
    this.id = uuid();
  }
}

@ObjectType()
@Entity()
export class Teacher extends BaseEntity {
  @Field(() => ID)
  @PrimaryColumn()
  id: string;

  @OneToMany(() => TeacherFaculty, (tf) => tf.teacher)
  facultyConn: Promise<TeacherFaculty[]>;

  @BeforeInsert()
  setId() {
    this.id = uuid();
  }
}


@Entity()
export class TeacherFaculty extends BaseEntity {
  @PrimaryColumn()
  teacherId: number;

  @PrimaryColumn()
  facultyId: number;

  @ManyToOne(() => Teacher, (teacher) => teacher.facultyConn, {
    primary: true,
  })
  @JoinColumn({ name: "teacherId" })
  teacher: Promise<Teacher>;

  @ManyToOne(() => Faculty, (faculty) => faculty.teacherConn, {
    primary: true,
  })
  @JoinColumn({ name: "facultyId" })
  faculty: Promise<Faculty>;
}

现在添加项目变得如此简单：

@Mutation(() => Teacher)
  async addTeacherToFaculty(
    @Arg('teacherId') teacher_id: string,
    @Arg('facultyId') faculty_id: string
  ): Promise<Teacher> {
    try {
     await TeacherFaculty.create({ teacherId:teacher_id , facultyId: faculty_id}).save();
    } catch (err) {
      console.log(err)          
    }
const teacher = await Teacher.findOne({where:{id:teacher_id}, relations:["facultyConn"]})
return teacher
}

【讨论】：