How to Return Only One Time Nested Object in DTO Using MapStruct

Описание: Discover how to achieve a clean and concise representation of nested objects in DTOs using MapStruct, focusing on effective mapping strategies and practical examples.
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How to Return Only One Time Nested Object in DTO Using MapStruct

When working with nested data structures in Java, particularly when using Data Transfer Objects (DTOs), it's common to run into situations where the nested relationships can create redundant object hierarchies. Today, we will tackle the problem of a nested object that references itself and explore how to use MapStruct to resolve it effectively.

Understanding the Problem

Consider a Java class Person that contains an instance of itself as a property named parent. Here’s what the class structure looks like:

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This structure allows you to represent complex relationships, such as family trees. However, when we try to convert a list of Person objects into their corresponding DTOs, we end up with an undesired output that includes multiple nested references to parents.

Example Data

Suppose we have the following list of Person objects:

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When converting this structure to DTOs, the output looks like this:

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As you can see, the parent references go back multiple levels, resulting in an unnecessarily deep object structure. What we want instead is to have a more concise representation:

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The Solution Using MapStruct

Step 1: Setting Up Your Mapper

To solve this problem, we can utilize MapStruct, a powerful annotation processor that simplifies the mapping process between Java objects. We'll create a mapper interface for our Person class.

Here's how you can set it up:

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Step 2: Explanation of the Mapper Code

Person to PersonDTO Mapping: The personToPersonDTO method is tasked with converting Person entities to PersonDto representations.

@ AfterMapping Annotation: This annotation indicates that the deleteGrandParents method is executed after the mapping completes. It is crucial for performing any additional logic needed post-mapping.

Deleting Grandparents: The logic within the deleteGrandParents method checks if the parent of the mapped PersonDto is not null. If it exists, we simply set its parent to null, effectively removing the grandparent reference from the DTO.

Conclusion

By using MapStruct and applying the @ AfterMapping logic, we can effectively control the mapping behavior to avoid returning unnecessary nested objects. This ensures that our DTO representations are simpler and more user-friendly.

With these techniques, you can cleanly handle nested structures in DTOs while leveraging the strengths of MapStruct to simplify your codebase. If you're dealing with complex data relationships in a Spring Boot application, implementing this pattern can significantly enhance your project's maintainability and clarity.

Happy coding!