Schema Validation

Step 1: Install Zod

1. Install Zod in your NestJS project:

   cd backend
   npm install zod

2. Optionally, install Zod typings for TypeScript support:

   npm install --save-dev @types/zod

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Step 2: Create a DTO for Validation

1. Define a Schema: Create a schema for validation using Zod. For example:

   import { z } from 'zod';
    
   export const CreateUserSchema = z.object({
     email: z.string().email(),
   });

2. Use the Schema in a DTO: Combine the schema with NestJS Data Transfer Object (DTO) patterns if needed:

   export class CreateUserDto {
     static schema = CreateUserSchema;
   }

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Step 3: Validate Data in a Controller

1. Update the Controller: Use the Zod schema to validate incoming data in your controller methods:

   import { Controller, Post, Body, BadRequestException } from '@nestjs/common';
   import { z } from 'zod';
   import { CreateUserSchema } from './schemas/create-user.schema';
    
   @Controller('user')
   export class UserController {
     @Post()
     async createUser(@Body() body: any) {
       const validationResult = CreateUserSchema.safeParse(body);
    
       if (!validationResult.success) {
         throw new BadRequestException('Invalid data: ' + validationResult.error.message);
       }
    
       return { email: validationResult.data.email };
     }
   }

The safeParse Method Explaination:

• The safeParse method checks the data against the schema and returns:
  • success: true: If the data is valid.
  • success: false: If the data is invalid, along with the error details.

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Step 4: Handle Validation Errors Globally (Optional)

1. Create a Custom Pipe: Create a validation pipe to centralize schema validation:

   import { PipeTransform, Injectable, ArgumentMetadata, BadRequestException } from '@nestjs/common';
   import { z, ZodSchema } from 'zod';
    
   @Injectable()
   export class ZodValidationPipe implements PipeTransform {
     constructor(private schema: ZodSchema) {}
    
     transform(value: any, metadata: ArgumentMetadata) {
       const result = this.schema.safeParse(value);
       if (!result.success) {
         throw new BadRequestException('Validation failed: ' + result.error.message);
       }
       return result.data;
     }
   }

2. Use the Pipe in a Controller: Apply the custom pipe directly to a controller method:

   @Controller('user')
   export class UserController {
     @Post()
     async createUser(
       @Body(new ZodValidationPipe(CreateUserSchema)) body: any,
     ) {
       return { email: body.email };
     }
   }

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Step 5: Test Your API

1. Start Your Application: Run the NestJS application:

   npm run start:dev

2. Send Test Requests: Use Postman, cURL, or any HTTP client to test the API:

   curl -X POST http://localhost:3000/user -H "Content-Type: application/json" -d '{"email": "invalid-email"}'

   You should receive a 400 Bad Request response for invalid data.

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Congratulations!

You’ve successfully implemented schema validation in NestJS using Zod. This approach ensures that your API routes are robust and secure by validating the incoming data. 🎉