dto-patterns

name	dto-patterns
description	Type and validation conventions for this Next.js project. Types live in modules/[name]/[name].types.ts, Zod schemas in modules/[name]/[name].validation.ts. Load when creating or modifying types, validation schemas, or shared interfaces.

Type & Validation Patterns

This is a plain Next.js app — no NestJS, no monorepo, no class-based DTOs.

Split per module

Each module owns its types and validation:

modules/[name]/
├── [name].types.ts       ← plain TypeScript interfaces/types
└── [name].validation.ts  ← Zod schemas for API boundary validation

Types ([name].types.ts)

export type Post = {
  id: string;
  title: string;
  content: string;
  authorId: string;
  createdAt: Date;
  updatedAt: Date;
};

export type CreatePostInput = {
  title: string;
  content: string;
  authorId: string; // set from JWT in route, not client input
};

export type UpdatePostInput = Partial<Omit<CreatePostInput, 'authorId'>>;

// With relations — used when repo queries include `with`
export type PostWithAuthor = Post & {
  author: { id: string; name: string };
};

Rules:

• Use type for unions/primitives, interface for object shapes
• Never infer types directly from Drizzle schema in components
• Use Omit<> to strip server-set fields (e.g. passwordHash, authorId)
• Add WithRelation variants when repo queries use with

Validation ([name].validation.ts)

import { z } from 'zod';

// Only fields the CLIENT sends — never authorId, id, or timestamps
export const createPostSchema = z.object({
  title: z.string().min(1).max(255),
  content: z.string().min(1),
});

export type CreatePostSchemaType = z.infer<typeof createPostSchema>;

export const updatePostSchema = createPostSchema.partial();

export type UpdatePostSchemaType = z.infer<typeof updatePostSchema>;

Rules:

• Schema = what the client sends; server-set fields (authorId, id, timestamps) excluded
• authorId is extracted from JWT in the route via getUserFromRequest(req)
• Always use .partial() for update schemas
• Prefer safeParse over parse — never let Zod throw in routes

Barrel export

Both types and validation are exported via the module's index.ts:

export * from './post.types';
export * from './post.validation';

Import at route/service level via the barrel:

import { createPostSchema, type CreatePostInput } from '@/modules/post';