Relations with multiple primary keys

I want to model a relation of two entities where the relation has some properties (eg. a Post has a many-to-many relation with Categories, but since the relation has some properties - like order or categerizedAt or whatever property you can imagine for such a relation - I have to introduce a join table I guess. I have tried to get the correct mapping with typeorm but failed:

• how to define the primary key in the jointable?
• persisting fails with [ERROR] [default] - Error: Entity PostCategoryRelation has multiple primary keys. This operation is not supported on entities with multiple primary keys at EntityMetadata.firstPrimaryColumn

First try:

@Table()
export class Post {

    @PrimaryGeneratedColumn()
    id: number;

    @Column()
    title: string;

    @Column()
    text: string;

    @OneToMany(type => PostCategoryRelation, postCategoryRelation => postCategoryRelation.post)
    categories: PostCategoryRelation[];
}

@Table()
export class PostCategory {

    @PrimaryGeneratedColumn()
    id: number;

    @Column()
    name: string;

    @OneToMany(type => PostCategoryRelation, postCategoryRelation => postCategoryRelation.category)
    posts: PostCategoryRelation[];
}

@Table()
export class PostCategoryRelation {
  @ManyToOne(type => Post, post => post.categories)
  @PrimaryColumn()
  post: Post;

  @ManyToOne(type => PostCategory, category => category.posts)
  @PrimaryColumn()
  category: PostCategory;

  @Column()
  addedByAdmin: boolean;

  @Column()
  addedByUser: boolean;
}

Did not work since PrimaryKey type cannot be determined. Next try:

@Table()
export class Post {

  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  title: string;

  @Column()
  text: string;

  @OneToMany(type => PostCategoryRelation, postCategoryRelation => postCategoryRelation.post)
  categories: PostCategoryRelation[];
}

@Table()
export class PostCategory {

  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @OneToMany(type => PostCategoryRelation, postCategoryRelation => postCategoryRelation.category)
  posts: PostCategoryRelation[];
}

@Table()
export class PostCategoryRelation {

  @PrimaryColumn('int', { name: 'id_post' })
  private postRef: number;

  @PrimaryColumn('int', { name: 'id_cat' })
  private catRef: number;

  @ManyToOne(type => Post, post => post.categories)
  @JoinColumn({ name: 'id_post', referencedColumnName: 'id' })
  post: Post;

  @ManyToOne(type => PostCategory, category => category.posts)
  @JoinColumn({ name: 'id_cat', referencedColumnName: 'id' })
  category: PostCategory;

  @Column()
  addedByAdmin: boolean;

  @Column()
  addedByUser: boolean;
}

Now I get the above mentioned [ERROR] [default] - Error: Entity PostCategoryRelation has multiple primary keys. This operation is not supported on entities with multiple primary keys at EntityMetadata.firstPrimaryColumn

What is the right way to model this?

[MichalLytek]

I was talking about similar behavior in #43. The solution is to create unique index on your foreign keys and create @PrimaryGeneratedColumn() in PostCategoryRelation

@Table()
@Index((relation: PostCategoryRelation) => [relation.post, relation.category], { unique: true })
export class PostCategoryRelation {
  @PrimaryGeneratedColumn()
  public readonly id: number;

  @ManyToOne(type => Post, post => post.categories)
  post: Post;

  @ManyToOne(type => PostCategory, category => category.posts)
  category: PostCategory;

  @Column()
  addedByAdmin: boolean;

  @Column()
  addedByUser: boolean;
}

The simplest solution with @ManyToOne(_type => Post, { primary: true }) isn’t implemented yet.

[pleerock]

@19majkel94 yes, it does