Maintain many to many relation

[Darkside73]

Suppose we have Post, Category and PostCategory entities:

@Entity('posts')
export class Post {
  @Fields.cuid()
    id = ''
  @Relations.toMany(() => PostCategory, 'postId')
    categories?: PostCategory[]
}

@Entity('categories')
export class Category {
  @Fields.cuid()
    id = ''
}

@Entity<PostCategory>('posts_categories')
export class PostCategory {
  @Fields.string({ required: true })
    postId = ''

  @Fields.string({ required: true })
    categoryId = ''

  @Relations.toOne<PostCategory, Category>(() => Category, 'categoryId')
    category?: Category

  @Relations.toOne<PostCategory, Post>(() => Post, 'postId')
    post?: Post
}

What is correct way to update post categories in edit form? Delete all and insert new?

const post = await repo.update(id, data)
const postCategories = repo.relations(post).categories
await postCategories.deleteMany({ where: { postId: id } })
await postCategories.insert(categories.map(categoryId => ({ categoryId })))

[noam-honig]

That's one option.
Another is to work a little harder to figure out which categories already exist, remove only the ones that are no longer needed and insert ones that are new

Here's a some code that I've writen a while back to do that in the crm-demo (we didn't have deleteMany back then)

https://github.com/remult/crm-demo/blob/master/src/Deals/Deal.entity.ts#L104