Complex relations TypeORM / MySQL

Question

I'm using TypeORM with MySQL, I have two Entity, User and Project:

@Entity()
class User {
    @PrimaryGeneratedColumn('uuid') 
    id: string;  

    @Column({})
    name: string;
}

@Entity()
class Project {
    @PrimaryGeneratedColumn('uuid') 
    id: string;  

    @Column({})
    name: string;
}

I would like to add a third entity, Invitation. An invitation is composed of the userId and the projectId as the key. A user can be invited to multiple projects but only once for each project. I also want to store the user who sends the invitation.

@Entity()
class Invitation {
    @PrimaryGeneratedColumn('uuid') 
    id: string;  

    @Column({})
    userID: string;

    @Column({})
    invitedById: string;

    @Column({})
    projectID: string;

    @Column({})
    otherInformations: string;

}

How can I achieve this using TypeORM Relations decorators?

Thanks, any help is appreciated, I'm still quite new to the ORM world.

Have a nice end of weekend.

Answer 1

This is what it looks like in the end:

@Entity()
class Invitation {
  @PrimaryGeneratedColumn("uuid")
  id: string;

  @Column({})
  projectID: string;

  @Column({})
  otherInformations: string;

  // Relations
  @ManyToOne(() => User, (user) => user.invitations)
  user: User;

  @ManyToOne(() => Project, (project) => project.invitations)
  project: Project;

  @ManyToOne(() => User, (user) => user.invited)
  invitedById: User;
}

@Entity()
class Project {
  @PrimaryGeneratedColumn("uuid")
  id: string;

  @Column({})
  name: string;

  @OneToMany(() => Invitation, (invitation) => invitation.project)
  invitations: Invitation[];
}

@Entity()
class User {
  @PrimaryGeneratedColumn("uuid")
  id: string;

  @Column({})
  name: string;

  @OneToMany(() => Invitation, (invitation) => invitation.user)
  invitations: Invitation[];

  @OneToMany(() => Invitation, (invitation) => invitation.invitedById)
  invited: Invitation[];
}

I'm trying to explain it but for a clearer explanation about relations, you can watch this video: https://www.youtube.com/watch?v=8kZ7W-bI5qQ&t=239s&ab_channel=BenAwad (just ignore the graphql part) or read the documentation about relations here: https://typeorm.io/#/relations

So your Invitation entity is the connection between the User and the Project as a many-to-many relation. You access the user via the @ManyToOne() decorator which creates a relation between many users and one invitation. The same with your Project entity:

  // Invitation.ts
  @ManyToOne(() => User, (user) => user.invitations)
  user: User;

  @ManyToOne(() => Project, (project) => project.invitations)
  project: Project;

In each Entity, you add the opposite relation to the Invitation entity

  // User.ts
  @OneToMany(() => Invitation, (invitation) => invitation.user)
  invitations: Invitation[];

  @OneToMany(() => Invitation, (invitation) => invitation.invitedById)
  invited: Invitation[];

  // Project.ts
  @OneToMany(() => Invitation, (invitation) => invitation.project)
  invitations: Invitation[];

Notice we use [] here because it's a ...ToMany() relation

invitedById is added the same way:

  // Invitation.ts
  @ManyToOne(() => User, (user) => user.invited)
  invitedById: User;

  // User.ts
  @OneToMany(() => Invitation, (invitation) => invitation.invitedById)
  invited: Invitation[];