Скачать или смотреть Overcoming Hibernate Performance Issues: Selecting Parent Entities Without Child Fetching

Discover how to optimize Hibernate queries and maintain persistence in entity relationships without fetching unnecessary child entities.
---
This video is based on the question https://stackoverflow.com/q/71829937/ asked by the user 'smanulla' ( https://stackoverflow.com/u/1993141/ ) and on the answer https://stackoverflow.com/a/71830408/ provided by the user 'v.ladynev' ( https://stackoverflow.com/u/3405171/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Hibernate 5 and JPA: select table without his children but maintain persistence on save

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Overcoming Hibernate Performance Issues: Selecting Parent Entities Without Child Fetching

Hibernate is a powerful Java framework for handling data persistence, but many developers face performance issues due to Hibernate's default fetching strategies. One common problem arises when attempting to load a parent entity while inadvertently pulling in its child entities as well. This post explores a common scenario and how to optimize the queries for efficient data retrieval.

The Problem

In a typical e-commerce application, you might have two models: Ordine (Order) and DettaglioOrdine (Order Detail). When saving an Ordine object, you also want to save its associated DettaglioOrdine objects. However, you find that performing a select query on the Ordine model is slow because Hibernate retrieves all child DettaglioOrdine entities by default.

Your Model Code

Here's a brief look at the key parts of your Ordine and Dettagliordine models:

[[See Video to Reveal this Text or Code Snippet]]

Your Query

The issue arises when executing a query like this:

[[See Video to Reveal this Text or Code Snippet]]

Performance Impact

The performance of this query can suffer dramatically if Hibernate is configured to eagerly fetch the child entities due to some inadvertent triggers, such as accessing methods in your data transfer objects that require fetching the child data.

The Solution

To resolve the performance issues arising from unnecessary fetching of child entities, you can follow these steps:

1. Maintain Lazy Fetching Configuration

Ensure that you declare the fetching strategy as FetchType.LAZY in both models, which you have done correctly:

For the Ordine entity, keep the fetch type as LAZY.

For the Dettagliordine entity, keep the fetch type as LAZY.

2. Inspect the unmarshall() Method

The real issue may lie within your unmarshall() method. Recognize that once you try to access any non-getter method (like toString()), Hibernate may trigger fetching of the lazy-loaded associations.

To fix this:

Avoid touching lazy-loaded collections within the unmarshall() method.

This will prevent unintended fetching of child entities whenever Ordine objects are accessed.

3. Move Logic Outside the Transactional Block

Consider refactoring your code to handle repetitive access patterns outside of any transaction:

[[See Video to Reveal this Text or Code Snippet]]

If this line is inside a transaction block and attempts to access dettagliordine, it will lead to a LazyInitializationException when you access the collection after the session is closed.

4. Enable Hibernate Logging

To trace fetching behaviors more effectively, enable Hibernate SQL logging. This allows you to see exactly when fetches happen, helping you pinpoint areas of accidental eager fetching.

5. Be Cautious with Debuggers

Be aware that debugging tools may invoke methods like toString(), inadvertently causing Hibernate to sever the lazy fetching configurations. If you need to debug, be cautious of what parts of your data model you expose to the debugger.

Conclusion

Optimizing Hibernate for performance requires careful handling of entity relationships and fetching strategies. By configuring models for lazy loading, vigilantly inspecting method calls, and refactoring transaction management, you can significantly improve performance. Following these steps ensures that you retrieve Ordine objects efficiently without the overhead of unnecessary DettaglioOrdine data.

By tackling the outlined issues and implementing these techniques, you can maintain persistence through saving while optimizing performance to meet your application's needs.