Validate Nested Objects Using Class Validator And Nestjs

When developing applications, it's crucial to ensure that the data being handled is accurate and complies with the expected structure. One common task in software development is validating nested objects to maintain data integrity. In this article, we will explore how to validate nested objects using Class Validator and NestJS, two powerful tools that can streamline this process and enhance the reliability of your applications.

**Setting Up Class Validator and NestJS**

Before we dive into the specifics of validating nested objects, let's ensure that we have Class Validator and NestJS set up in our project. Class Validator is a library that provides decorators and functions to validate class instances. NestJS, on the other hand, is a powerful framework built on top of Node.js that simplifies the development of server-side applications.

To get started, install Class Validator and class-transformer by running the following command:

Bash

npm install class-validator class-transformer

Next, make sure you have NestJS installed in your project. If not, you can set up a new NestJS project using the Nest CLI:

Bash

nest new project-name

**Creating Nested Objects for Validation**

To demonstrate how to validate nested objects, let's create a sample data structure that contains nested objects. Suppose we have a user entity that consists of a name, email, and address. The address itself is an object with street, city, and zip code properties.

Here's an example of how the data structure might look in TypeScript:

Typescript

import { IsEmail, IsNotEmpty, ValidateNested } from 'class-validator';
import { Type } from 'class-transformer';

class Address {
    @IsNotEmpty()
    street: string;

    @IsNotEmpty()
    city: string;

    @IsNotEmpty()
    zipCode: string;
}

class User {
    @IsNotEmpty()
    name: string;

    @IsEmail()
    email: string;

    @ValidateNested()
    @Type(() =&gt; Address)
    address: Address;
}

In this example, we defined two classes, Address and User, using Class Validator decorators to specify validation rules for each property. The `@ValidateNested()` and `@Type(() => Address)` decorators are used to validate the nested Address object within the User entity.

**Performing Validation in NestJS Controllers**

Now that we have our data structures in place, let's see how we can perform validation in a NestJS controller. First, inject the `ValidationPipe` from the `@nestjs/common` package into your controller constructor:

Typescript

import { Controller, Post, Body, UsePipes, ValidationPipe } from '@nestjs/common';

@Controller('users')
export class UserController {
    @Post()
    @UsePipes(new ValidationPipe())
    createUser(@Body() user: User) {
        // Process validated user object
    }
}

In this code snippet, we applied the `ValidationPipe` to the `createUser` method, which automatically validates the incoming `user` object based on the rules defined in the User class. If the validation fails, NestJS will handle the error and prevent the request from being processed further.

**Conclusion**

By utilizing Class Validator and NestJS, you can easily validate nested objects in your applications, ensuring that your data is accurate and consistent. These tools provide a seamless way to enforce validation rules and maintain data integrity throughout your software development process. Incorporate these practices into your projects to enhance the robustness and reliability of your applications.

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