Understanding OpenAPI Optional Request Objects with Mandatory Fields

A comprehensive guide on how to manage `optional` OpenAPI request objects with mandatory fields using Spring Boot and validation techniques.
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Managing Optional Request Objects with Mandatory Fields in OpenAPI

In today's tech landscape, designing APIs with clarity and efficiency is essential. A common scenario developers face is the challenge of handling optional request objects that carry mandatory fields. In this guide, we will address the nuances of OpenAPI's specifications, particularly in a Spring Boot environment, to help you manage these object requirements effectively.

The Problem

As you dive into using OpenAPI (version 3.0.1), you might encounter the requirement to have an object that is not mandatory overall but must fulfill specific mandatory conditions if any fields are included. For instance, consider a situation where you have a ComplexObject that includes Sorting and Pagination as optional parameters. However, once included, all fields must be filled out.

Here’s a sample structure of your OpenAPI paths and components:

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Upon implementation, you may notice that even without any parameters being sent, instances of the Pagination and Sorting classes are being created, leading to validation failures.

The Solution

While the OpenAPI generator is somewhat limited in this regard, there is a workaround using default values. Below is an illustration of how to structure the Sorting and Pagination objects effectively:

Step 1: Utilize Default Values

You can specify default values in the YAML schema to prevent the creation of null instances when parameters are not sent. Here's how you can modify the Pagination and Sorting definitions:

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Step 2: Understand Generated Code Behavior

When you set defaults for the properties, you avoid scenarios where required fields end up being null. Here's how the generated Java code will look after using defaults:

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

Important Note on Validation

Interestingly, the validation logic of the sorted property works as intended regardless of default specifications or field requirements. You can observe how required settings yield different outcomes on Java code generation:

Without ‘required’:

The field is nullable and defaults to null.

With ‘required’:

The field is instantiated as an empty list if not populated via the API request.

This ensures you still implement validation effectively without risking unnecessary null fields.

Conclusion

Handling optional request objects that stipulate mandatory fields requires a good understanding of OpenAPI specifications and the capabilities of your tools. By leveraging default values and understanding how the generated code behaves, you can create robust and reliable APIs that meet your functional requirements.

Whether you choose to adjust your OpenAPI definitions or handle validations programmatically, the approach presented here will guide you in building seamless API integrations.

If you have any further questions or need assistance, feel free to reach out!