Schema definition in NextJS

Introduction

Schema definition helps you describe the shape and rules of your data clearly. It makes sure your app uses data correctly and avoids errors.

When you want to validate user input before saving it.

When you need to define the structure of data sent between server and client.

When working with databases to ensure data follows expected formats.

When building APIs to document and enforce data contracts.

When you want to catch mistakes early by checking data shapes.

Syntax

NextJS

import { z } from 'zod';

const schema = z.object({
  name: z.string(),
  age: z.number().int().positive(),
  email: z.string().email().optional()
});

This example uses zod, a popular schema library in Next.js projects.

Each field defines the expected type and rules, like string, number, or optional fields.

Examples

Defines a user with a username and password, both strings with minimum lengths.

NextJS

const userSchema = z.object({
  username: z.string().min(3),
  password: z.string().min(8)
});

Defines a product with an ID, a non-negative price, and optional tags as an array of strings.

NextJS

const productSchema = z.object({
  id: z.string(),
  price: z.number().nonnegative(),
  tags: z.array(z.string()).optional()
});

Defines a response that can be either success with data or failure with an error message.

NextJS

const responseSchema = z.union([
  z.object({ success: z.literal(true), data: z.any() }),
  z.object({ success: z.literal(false), error: z.string() })
]);

Sample Program

This code defines a user schema and checks if userData matches it. If valid, it prints the user data. If not, it shows errors.

NextJS

import { z } from 'zod';

const userSchema = z.object({
  name: z.string(),
  age: z.number().int().positive(),
  email: z.string().email().optional()
});

// Example data to validate
const userData = {
  name: 'Alice',
  age: 30,
  email: '[e-mail]'
};

try {
  const validatedUser = userSchema.parse(userData);
  console.log('Valid user:', validatedUser);
} catch (e) {
  console.log('Validation error:', e.errors);
}

Important Notes

Always validate data before using it to avoid bugs and security issues.

Schema libraries like zod integrate well with Next.js and TypeScript for better developer experience.

Optional fields let you accept data that may or may not be present.

Summary

Schema definition describes the shape and rules of your data.

It helps catch errors early by validating data before use.

Using libraries like zod makes schema definition easy and clear in Next.js projects.