Resolving Nested Property Mapping Issues in ModelMapper

Описание: Learn how to fix the issue of incorrect nested property mapping in `ModelMapper` when dealing with similar property names. This step-by-step guide offers a custom solution to ensure accurate mapping.
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This video is based on the question https://stackoverflow.com/q/58698325/ asked by the user 'andkov' ( https://stackoverflow.com/u/11758992/ ) and on the answer https://stackoverflow.com/a/77885949/ provided by the user 'Marwen Mighri' ( https://stackoverflow.com/u/4636142/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Nested Property Mapping Issues in ModelMapper

When working with object mapping in Java, especially with DTOs (Data Transfer Objects) and entities, one commonly used library is ModelMapper. A frequent challenge developers face is when ModelMapper incorrectly maps properties of nested objects that share the same name. This guide will explore this issue and how to resolve it effectively.

The Problem

Suppose you have a Child entity class and a ChildDTO class where both contain properties with the same name — in this case, name. If you attempt to use ModelMapper to map a ChildDTO to a Child entity, it inadvertently updates properties in nested classes, such as Parent.name, instead of just Child.name.

Example Classes

To illustrate this, consider the following classes:

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When you perform the mapping:

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Unexpected Behavior

This approach leads to both Child.name and Parent.name being updated to "new name" instead of just Child.name. This occurs despite using the STRICT matching strategy.

The Solution

To address this, we need to implement a custom matching strategy that prevents ModelMapper from incorrectly mapping the nested properties.

Custom Matching Strategy

Here’s how you can create your custom matching strategy:

Extend the Standard Matching Strategy: Start by creating a new class that extends MatchingStrategies.STANDARD.

Override the matches Method: In this method, we will specify custom conditions for matching properties based on their source and destination.

Here’s an example implementation:

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Applying the Custom Strategy

You can utilize your new matching strategy as follows:

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Now, when you run your mapping with the Child DTO and Child object, the properties will map as intended:

Child.ref will correctly remain "CHILD-REF"

Parent.ref can be set separately to "PARENT-REF"

Conclusion

By customizing the matching strategy for ModelMapper, you can maintain greater control over property mappings, especially in cases where nested properties have similar names. This solution not only resolves the immediate mapping issue but also enhances the maintainability of your Java application.

Now, you can confidently use ModelMapper without the fear of inadvertently modifying nested object properties. Happy coding!