Скачать или смотреть How to Perform an Envers Query Using Spring's EntityManager in JHipster

Learn how to efficiently create a service in JHipster that performs an `Envers` audit query by reusing the existing database session with proper dependency injection.
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This video is based on the question https://stackoverflow.com/q/62454326/ asked by the user 'adejoux' ( https://stackoverflow.com/u/568757/ ) and on the answer https://stackoverflow.com/a/62465776/ provided by the user 'Gaël Marziou' ( https://stackoverflow.com/u/93960/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Perform an Envers Query Using Spring's EntityManager in JHipster

In today's guide, we'll tackle a common problem encountered when integrating JHipster applications with Hibernate Envers for auditing purposes. Specifically, we will address how to efficiently perform an audit query using an existing database session from a service using Spring's EntityManager.

The Problem Overview

In many applications, particularly those that require strict auditing capabilities, Envers can be an incredibly useful tool. However, developers may run into issues when trying to access the EntityManager to perform queries. A common situation involves encountering a Java NullPointerException when attempting to use the EntityManager without proper dependency injection.

The Scenario

You are creating an audit service called SecurityAuditService to fetch audit data using Envers. After implementing the service, you find that the EntityManager is null, leading to a NullPointerException when you try to run your queries. Here’s a snippet of the code you might have:

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As you can see, without proper initialization, you're facing issues with the entityManager.

The Solution

To resolve the issue, the first step is to ensure that Spring properly manages the EntityManager. Here, we outline the necessary changes to your SecurityAuditService.

Step-by-Step Guide to Fix the Issue

Constructor Injection

One of the most effective practices in Spring is constructor-based dependency injection. This ensures that your EntityManager is always initialized before it is used.

Here’s how you can modify your service:

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Use the @ Autowired Annotation

Alternatively, you can choose to just annotate the EntityManager with @ Autowired. This approach is straightforward but less preferred compared to constructor injection for better testability.

Here’s how this modification would look:

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Testing Your Service

Make sure to write tests to confirm that the EntityManager is being injected correctly and that your audit queries run without any issues.

Final Thoughts

By following these structured steps, you can ensure that your EntityManager is properly initialized and available for use in your service, effectively bypassing any NullPointerException issues. Adopting best practices such as constructor injection not only makes your code cleaner but also enhances maintainability and testability.

If you're working with JHipster and Hibernate Envers, these adjustments will certainly aid in creating an efficient auditing service.

Do you have any further questions or challenges you are facing? Feel free to share in the comments below!