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Learn to update both parent and child entities in Spring Boot using JPA without running into common pitfalls.
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This video is based on the question https://stackoverflow.com/q/65083182/ asked by the user 'Abraham Arnold' ( https://stackoverflow.com/u/11813880/ ) and on the answer https://stackoverflow.com/a/65086349/ provided by the user 'Jens Schauder' ( https://stackoverflow.com/u/66686/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Update Child Entity with Parent Entity in Spring Boot?

Updating related entities in a Java Spring Boot application can often lead to confusion, particularly when dealing with a parent-child relationship using JPA and Hibernate. In this post, we'll delve into a common problem: how to update a parent entity along with its child entity—the User and Contact entities in our case—without encountering persistence context issues.

The Problem

When attempting to update both entities simultaneously, many developers hit a stumbling block, often resulting in the following error:

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This issue arises when you try to manage two instances of an entity that represent the same database record, leading to conflicts in the persistence context.

Example Entities

Here’s a quick overview of our User (Parent) and Contact (Child) entities:

User.java:

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Contact.java:

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When updating these entities in your service, you might encounter a frustrating roadblock.

The Solution

To resolve this problem, we need to ensure that we’re not creating new instances of entities that already exist in the persistence context. The key is to modify the existing instance rather than trying to reassign it.

Steps to Correctly Update Entities

Fetch the existing entity: Load the existing User entity from the database using its ID.

Update the fetched entity: Instead of setting the ID of the new user instance, we directly update the fields of the curUser entity.

Manage the Contact reference correctly: Since Contact is tied to User, we need to handle it while updating as well.

Here’s how your update method should look:

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Important Notes

Do not change the ID: The line user.setId(curUser.get().getId()); should be replaced with simply setting the ID directly to the incoming entity:

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Single Instance: It’s crucial to maintain a single instance of your entity in the persistence context. This means either modify the loaded entity directly or handle detached entities appropriately without mixing references.

Check for Presence: Always check if the user exists before proceeding with updates to avoid NoSuchElementException.

By following these best practices, you can efficiently update both parent and child entities within your Spring Boot application while avoiding common JPA pitfalls.

Conclusion

Updating a parent and its child entity in Spring Boot using JPA doesn’t have to be complex. By understanding the persistence context and properly managing entity states, you can prevent errors and ensure seamless data handling. Keep these guidelines in mind, and your application will handle updates gracefully.