Creating a Spring Search DTO with Defined Value Constraints

Learn how to implement a Spring Data Transfer Object (DTO) with strict validation for a defined list of values using enums. Discover practical coding examples and step-by-step explanations.
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Creating a Spring Search DTO with Defined Value Constraints

In application development, especially when using frameworks like Spring, it's crucial to ensure that the data you handle conforms to specific rules and formats. One common requirement is to create a Data Transfer Object (DTO) that restricts certain fields to a predefined list of acceptable values. This article will explain how to implement such a feature in a Spring application.

The Problem

Our goal is to create a DTO that includes a field, type, which should only accept specific values: 'approved', 'new', and 'closed'. The standard approach involves using annotations to enforce validation rules. However, we need to ensure that the field can strictly adhere to this defined list, preventing any invalid data from being accepted.

Initial DTO Structure

Let’s start with a basic DTO structure:

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

In this initial design, the type field can take in any string. This does not enforce our requirement effectively.

The Solution

To rectify this, we can leverage Java enums to specify a fixed set of values. Here’s how we can implement it:

Step 1: Define the Enum

First, let's define an enum that represents our allowed values:

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

By using an enum, we constrain the type field to accept only the defined constants.

Step 2: Update the DTO

Next, we need to modify our DTO to use this enum:

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

With these changes, the type field can now only accept TypeEnum.APPROVED, TypeEnum.NEW, or TypeEnum.CLOSED. If any other string is assigned, it would lead to a compilation error, ensuring strong type safety.

Step 3: Enriching the Enum with Descriptions

To add further functionality and control over the case sensitivity of our values, we can enhance our enum with descriptive values:

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

With this implementation, each enum constant has a string description associated with it. The method fromDesc(String desc) allows us to retrieve the corresponding enum value by providing the string representation.

Step 4: Using the Enum

You can now retrieve the enum value using a lowercase string:

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

This functionality allows you to convert strings to enum values safely and consistently.

Conclusion

By using Java enums in our DTO, we can enforce strict validation constraints for specific fields, ensuring that our application only processes valid and defined data. This approach not only enhances the reliability of your application but also improves the readability and maintainability of your code.

Implementing validation with enums is a powerful pattern that can be applied across various areas in Spring applications. With this guide, you can confidently define your DTOs and maintain robust data integrity.