how can i access nested properties for CASL conditions - node.js

Question

I can't seem to access the nested object with the condition rule.
i want a user to have access to delete an article if the article's comment has the same id as the user.
these are just some made up classes to test...
here is my code:
import { defineAbility, AbilityBuilder } from '#casl/ability';
import { Ability, AbilityClass, ExtractSubjectType, InferSubjects } from '#casl/ability';
export class Article {
static readonly modelName = "Article";
static readonly __typename = "Article";
constructor( id: number,
title: string,
content: string,
user: User,
comment: Comment) {
this.id = id
this.title = title
this.content = content
this.user = user
this.comment = comment
}
id: number
title: string
content: string
user: User
comment: Comment
}
export class User {
static readonly modelName = "User"
static readonly __typename = "User";
constructor (id: number,
name: string,
comment: Comment) {
this.id = id
this.name = name
this.comment = comment
}
id: number
name: string
comment: Comment
}
export class Comment {
static readonly modelName = "Comment"
static readonly __typename = "Comment";
constructor(id: number,
content: string,
authorId: number) {
this.id = id
this.content = content
this.authorId = authorId
}
id: number
content: string
authorId: number
}
type Action = 'create' | 'read' | 'update' | 'delete';
type Subjects = InferSubjects<typeof Article | typeof Comment| typeof User, true>;
export type AppAbility = Ability<[Action, Subjects]>;
export function createForUser(user: User) {
const { can, cannot, build } = new AbilityBuilder<
Ability<[Action, Subjects]>
>(Ability as AbilityClass<AppAbility>);
can('delete', Article, { comment: {id: user.comment.id}})
return build({
detectSubjectType: item => item.constructor as ExtractSubjectType<Subjects>
});
}
and im testing it with:
const comment = new Comment(0, 'a', 0)
const user = new User(1, 'sd', comment);
const article = new Article(2, 'sd', 'asd', user, comment)
const ability = createForUser(user);
console.log(ability.can('delete', article))// false
i saw somewhere that i need to do somthing like this:
can('delete', Article, { 'comment.id': user.comment.id})
but when i do is says 'Object literal may only specify known properties, and ''comment.id'' does not exist in type 'string[]'

Answer 1

You can find “Nested fields with dot notation” section on https://casl.js.org/v5/en/advanced/typescript useful. In short, when you use for notation to define conditions together with typescript, you need to create a custom type:
type FlatArticle = Article & {
'comment.id': Article['comment']['id']
};
can<FlatArticle>('read', Article, { 'comment.id': 1 });

Answer 2

Ended up solving it like this:
export enum Action {
Manage = 'manage',
Create = 'create',
Read = 'read',
Update = 'update',
Delete = 'delete',
}
export type Subject = InferSubjects<typeof Article |
typeof Comment |
typeof User |
'all';
export type AppAbility = PureAbility<[Action, Subject]>;
export const AppAbility = Ability as AbilityClass<AppAbility>;
and then defining rules like this:
createForUser(user: User) {
const { can, cannot, build } = new AbilityBuilder(AppAbility);
can(Action.Read, Article, { 'comment.id': 1 });
return build({
detectSubjectType: item => item.constructor as ExtractSubjectType<Subject>
});
}