Creating a Mapper from Entity to DTO in Kotlin: Navigating Nested Structures

Learn how to effectively create a mapper from entity to DTO in Kotlin, especially when dealing with nested structures like lists of images. This guide simplifies the process and resolves common type mismatch errors.
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How to Create a Mapper from Entity to DTO in Kotlin with Nested Structures

When working with the Kotlin programming language in a Spring Boot application, you may encounter the need to create a mapper that translates complex data structures, such as entities and Data Transfer Objects (DTOs). This is especially relevant when dealing with nested objects. In this post, we'll explore a specific use case involving GalleryBlock and Image entities, and how to effectively map them to their corresponding DTO representations.

The Problem: Mapping Nested Entities

Suppose you have the following entities:

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And their corresponding DTO classes:

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To implement the mapping, you created an interface:

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

You also created a mapper for the Image class:

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

However, when you attempted to map GalleryBlock to GalleryBlockDto, you faced a type mismatch issue because you were implicitly trying to pass Image instances instead of ImageDto instances.

The Solution: Injecting the ImageMapper

To resolve this issue, we need to modify the GalleryBlockMapper to utilize the ImageMapper. Here’s how you can do it:

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

Breaking it Down

Injecting the ImageMapper: This allows you to use ImageMapper to convert each Image instance to ImageDto within the GalleryBlockMapper.

Mapping the Images: In the fromEntity method, we utilize Kotlin’s map function to iterate over each Image in the images list of the GalleryBlock. It converts the Image entities into ImageDto instances.

Handling Null Values: If your Image list can contain nulls, make sure to handle this safely by using the !! operator or an alternative null-safety strategy if necessary.

Returning the DTO: Finally, we construct and return the GalleryBlockDto using the mapped images and the sortIndex.

Conclusion

By implementing the mapper correctly, you can efficiently handle nested entity structures in Kotlin while avoiding common pitfalls like type mismatches. Creating interfaces and utilizing dependency injection allows for a clean and maintainable code structure, making mapping between entities and DTOs seamless and straightforward.

With this guide, you should now have a better understanding of how to create a nested DTO mapper in Kotlin using Spring Boot. Feel free to reach out for further clarification or specific use cases you may have!