Скачать или смотреть Transforming JSON Property Names with NestJS: A Guide Using ValidationPipe and Custom Pipes

Learn how to transform JSON property names in NestJS using a custom pipe and `ValidationPipe`. Map incoming payloads accurately to your TypeScript DTOs while ensuring proper validation.
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Transforming JSON Property Names with NestJS: A Guide Using ValidationPipe and Custom Pipes

In modern web applications, particularly those developed with TypeScript and frameworks like NestJS, handling inbound JSON payloads is crucial. When integrating with legacy systems, you may encounter a mix of upper and lower case property names within incoming JSON objects. You may want to ensure that all incoming properties adhere to a consistent camel-case format for compatibility with your new API standards.

In this guide, we will dive into how you can transform property names in incoming JSON requests using NestJS's ValidationPipe and create a custom pipe to achieve the desired transformations while maintaining proper validation.

Understanding the Problem

Picture this scenario: you're building a new NestJS API, but the incoming JSON property names from a legacy system are inconsistent, such as:

"propertyone"

"PROPERTYTWO"

"PropertyThree"

You want to correctly map these to camel-case properties in your TypeScript Data Transfer Object (DTO):

"propertyOne"

"propertyTwo"

"propertyThree"

Key Challenges

Transforming properties before validation: The built-in ValidationPipe processes the payload for validation before any transformation occurs, leading to validation errors when the property names do not match.

Inconsistent casing: Property names from the JSON payload may not align with your DTO expectations, causing unnecessary data handling clashes.

Nested objects: Even when transforming simple properties works, issues may arise with nested object properties that don't match the DTO definitions.

Solution Overview

A successful approach involves creating a custom validation pipe that handles the mapping of incoming properties directly to your DTO. This allows you to control the order in which transformation and validation occur, ensuring no mismatches hinder the validation process.

Step 1: Create a Custom Pipe

This custom pipe will explicitly map properties from the incoming JSON payload to the desired properties in your DTO. Here’s a basic implementation:

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Step 2: Modify the Incoming DTO

Ensure your DTO is defined correctly. The properties should align with how you want to handle validation.

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Use Custom and Validation Pipes Together

Integrate the RequestConverterPipe into your controller to ensure that it executes before the ValidationPipe. This is essential for the correct application of validation.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By creating a custom mapping pipe, you can manage how incoming properties are transformed and ensure they are validated correctly. This method not only resolves property naming issues but also enhances code maintainability, preventing your new API from being tightly coupled with the legacy system's naming conventions.

Staying consistent with the camel-case format will help you enforce standards in your TypeScript models and keep your applications clean and efficient. If you encounter similar challenges with property name transformations, consider implementing a solution using a custom validation pipe in your NestJS applications!