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Discover how to resolve empty object returns when converting entities to bean classes using Model Mapper in Java. Learn effective solutions to enhance your mapping strategy.
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Solving Entity to Bean Mapping Issues with Model Mapper in Java

One common challenge that developers face when working with Java applications is mapping entities to DTO (Data Transfer Object) classes effectively. This situation becomes particularly tricky when the entity contains complex types, such as embedded objects, which do not readily map to their corresponding fields in the DTO.

In this guide, we'll explore a specific issue where a developer encounters an empty object when converting an entity to a bean using Model Mapper. We'll break down the problem, explain why it occurs, and provide a straightforward solution that can enhance your mapping strategy.

Understanding the Problem

The issue arises when attempting to map an entity with complex nested properties to a DTO class using Model Mapper. In this case, the developer observed that while basic properties like UUID were being mapped correctly, the additional property of type AdditionalPropertyDto was returning null.

Here's a quick overview of the classes involved:

DTO Class: SettingDto

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Nested DTO Class: AdditionalPropertyDto

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Entity Class: SettingEntity

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Why Does This Happen?

The primary reason for the null value in the additionalProperty field in SettingDto is that Model Mapper is unable to directly convert the Object type in the entity to the specific AdditionalPropertyDto type in the DTO. When it encounters complex types, the mapping may not occur as expected, leading to empty or null results.

Proposed Solution

To resolve this issue, we can take an alternative approach by using ObjectMapper in conjunction with Model Mapper. Here’s how to effectively map the complex property separately:

Step-by-Step Implementation

Set up Model Mapper for Basic Fields
Use Model Mapper to handle the mapping of the UUID and any other simple fields.

Handle Complex Objects with ObjectMapper
For the additional property, utilize ObjectMapper to map the additionalProperty from the entity into an AdditionalPropertyDto object.

Here's a sample implementation:

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Explanation of Code

Initial Mapping: Starts with a basic mapping of SettingEntity to SettingDto, where simple fields like settingUUID are copied over.

JSON Handling: The additional property of type Object is converted into a JSON string and then mapped back to the AdditionalPropertyDto class.

Error Handling: Includes try-catch blocks to manage any exceptions that might occur during the conversion processes.

Conclusion

Mapping entities to beans can be quite straightforward when dealing with simple data types. However, it can become complex when handling nested objects or other intricate structures. By adopting a dual approach with Model Mapper for basic fields and ObjectMapper for complex types, we can effectively resolve issues where data doesn’t map as expected.

By following the solution outlined above, you can enhance your Java application’s data mapping capabilities and ensure that all properties, including nested ones, are correctly populated. Happy coding!