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Building Secure RESTful APIs with NestJS: A Practical Guide

Handling Many-to-Many Relationships

Explore how to define and manage many-to-many relationships between entities using TypeORM with NestJS. Understand entity decorators, saving linked records, and retrieving related data using user and role models. Learn the difference between bidirectional and unidirectional relations and test the implementation with practical API calls.

We'll cover the following...

A many-to-many relationship

In this lesson, we’ll learn how to manage many-to-many relationships using TypeORM.

A many-to-many relationship is typical when dealing with complex data structures. Below is an example of the user and role entities. A user entity can have multiple roles to define their access, and a role entity can be assigned to multiple users.

A many-to-many relationship between user and role
A many-to-many relationship between user and role

In the illustration above, there is a user-roles-role intermediate table. It’s to link the primary keys of the user and role tables.

Define the entities

First, we need to define the user and role entities.

TypeScript 4.9.5
// user.entity.ts
@Entity('user')
export class UserEntity {
  @PrimaryGeneratedColumn()
  id: number;
    ...
  @ManyToMany(() => RoleEntity, (role) => role.users, {
    eager: true,
    cascade: ['insert', 'update'],
  })
  @JoinTable()
  roles: RoleEntity[];
}
// role.entity.ts
@Entity('role')
export class RoleEntity {
  @PrimaryGeneratedColumn()
  id: number;
  @Column()
  name: string;
  @ManyToMany(() => UserEntity, user => user.roles,  {
    cascade: ['insert', 'update'],
  })
  users: UserEntity[];
}

Two decorators are used to define the many-to-many relationship between the two entities.

  • @ManyToMany: This specifies the many-to-many relationship between ...