Validation

In Bedstack, validation is not just an afterthought—it's a core part of the architecture. We use ArkType to ensure that data is valid at the "edge" (the Controller) and throughout the application.

The Role of DTOs

Data Transfer Objects (DTOs) define the shape of data entering and leaving your application. In Bedstack, every DTO is an ArkType schema.

Defining an Input DTO

Input DTOs are used in POST, PUT, and PATCH requests. ArkType allows you to define these using a concise string-based syntax or a more traditional object-based one.

import { type } from 'arktype';

export const CreatePostDto = type({
  title: 'string >= 3',
  content: 'string',
  'tags?': 'string[]', 
});

import { type } from 'arktype';

export const CreatePostDto = type({
  title: type('string').and('3 <= length <= 100'),
  content: 'string',
  'tags?': 'string[]',
}).describe('A schema for creating a new post');

Validation at the Edge

By using Elysia's native support for ArkType, validation happens automatically before your controller logic is ever executed.

import { CreatePostDto } from './dto/create-post.dto';

export const postsController = new Elysia({ prefix: '/posts' })
  .post('/', ({ body }) => {
    // 'body' is guaranteed to match CreatePostDto here
    return postsService.create(body);
  }, {
    body: CreatePostDto
  });

Why This Architecture?

1. Single Source of Truth: Your validation schema is your TypeScript type.
2. Instant Feedback: Detailed error messages are generated automatically and sent back to the client.
3. Performance: ArkType's JIT-optimized validation is significantly faster than libraries like Zod or Joi.
4. Security: Strict validation at the Controller layer prevents malformed or malicious data from reaching your business logic or database.

Advanced Patterns

For complex validation, you can use ArkType's logical operators or custom regex:

export const UsernameSchema = type("string")
  .and("3 <= length <= 20")
  .and(regex(/^[a-z0-9_]+$/))
  .describe("3-20 characters, lowercase letters, numbers, and underscores");