NestJS: Validation

Zod schemas

Define schemas and attach to routes:

import { z } from 'zod';

export const createPostSchema = z.object({
  title: z.string().min(1),
  content: z.string().optional(),
  published: z.boolean().optional().default(false),
  tags: z.array(z.string()).optional().default([]),
});

export const updatePostSchema = z.object({
  title: z.string().min(1).optional(),
  content: z.string().optional(),
  published: z.boolean().optional(),
});

@CrudController({
  model: PostEntity,
  routes: {
    create: { schema: createPostSchema },
    update: { schema: updatePostSchema },
  },
})

class-validator DTOs

Install class-validator and class-transformer:

npm install class-validator class-transformer

Define DTOs:

import { IsBoolean, IsOptional, IsString, MinLength } from 'class-validator';

export class CreatePostDto {
  @IsString()
  @MinLength(1)
  title: string;

  @IsOptional()
  @IsString()
  content?: string;

  @IsOptional()
  @IsBoolean()
  published?: boolean;
}

@CrudController({
  model: PostEntity,
  routes: {
    create: { schema: CreatePostDto },
  },
})

Unified error format

Both Zod and class-validator produce the same error format:

{
  "statusCode": 422,
  "message": "Validation failed",
  "errors": [
    { "code": "invalid_type", "message": "Required", "path": ["title"] },
    { "code": "invalid_type", "message": "Expected number", "path": ["authorId"] }
  ]
}

Validation pipeline

Order of processing for create/update:

1. Validate body against schema (Zod or class-validator)
2. DtoMapper toCreateInput / toUpdateInput (if configured)
3. Hooks beforeCreate / beforeUpdate
4. Service create / update