Posted on June 6, by vladmihalcea. As previously explained , using the JPA entity business key for equals and hashCode is always best choice.
However, not all entities feature a unique business key, so we need to use another database column that is also unique, as the primary key. But using the entity identifier for equality is very challenging, and this post is going to show you how you can use it without issues. When it comes to implementing equals and hashCode , there is one and only one rule you should have in mind:.
Equals and hashCode must behave consistently across all entity state transitions. To test the effectiveness of an equals and hashCode implementation, the following test can be used:.
The isbn property is also a NaturalId , therefore, it should be unique and not nullable. Both equals and hashCode use the isbn property in their implementations. For more details about the NaturalId annotation, check out this article. What if our entity does not have any column that can be used as a NaturalId?
The first urge is to not define your own implementations of equals and hashCode , like in the following example:. The original entity is not equal with the one returned by the merge method because two distinct Object s do not share the same reference. When the entity was first stored in the Set, the identifier was null.
Information-Flow Analysis of Hibernate Query Language | SpringerLink
After the entity was persisted, the identifier was assigned to a value that was automatically generated, hence the hashCode differs. For this reason, the entity cannot be found in the Set after it got persisted. To address the previous issue, there is only one solution: the hashCode should always return the same value:. Also, when the entity identifier is null , we can guarantee equality only for the same object references.
Otherwise, no transient object is equal to any other transient or persisted object. With this implementation, the equals and hashCode test runs fine for all entity state transitions. The reason why it works is that the hashCode value does not change, hence, we can rely on the java. Object reference equality as long as the identifier is null. If you enjoyed this article, I bet you are going to love my Book and Video Courses as well.
The entity identifier can be used for equals and hashCode , but only if the hashCode returns the same value all the time.
This might sound like a terrible thing to do since it defeats the purpose of using multiple buckets in a HashSet or HashMap. However, for performance reasons, you should always limit the number of entities that are stored in a collection. You should never fetch thousands of entities in a OneToMany Set because the performance penalty on the database side is multiple orders of magnitude higher than using a single hashed bucket.
All tests are available on GitHub. This is not comprehensive, but it's light weight and concise writing, makes it a good choice for learning Hibernate. It also has couple of project like application, which helps to learn Hibernate development. You can also use this book to setup a fully hibernate based Java development environment including Spring and Eclipse.
It's not much different than others two, and if you have read the previous titles, than you probably don't need this. But in case, you have difficulty in connecting with previous books, than you can try this one. One of the good thing about this hibernate book is that it covers Hibernate 3. One of the positive point of this books are case studies, which explains key relationship concepts including one-to-many and many-to-many relationships from top to bottom.
Overall, only use this book, if you are not able to connect to Hibernate Made easy and Harnessing Hibernate, otherwise, you have enough at beginners level. This book teaches a lot about fetching strategies, caching, transactions and best practices in database design and ORM techniques.
I recommend this book at least a one read for any serious Java Hibernate developer, to get complete picture of Hibernate.
This book is over pages, which is not easy to read, but it definitely deserver a look for later reference. Similar to Spring recipes : A Problem solution approach, this book teaches you hibernate by introducing a problem and then solving it. This method can work for many developers, and if you have enjoyed previous books on this series, you will going to like this one as well.
#REVIEW: High-Performance Java Persistence Video Course from Vlad Mihalcea
Every single recipe is explained well with proper code example and decent explanation. One advantage, which I personally feel, while reading this book is comparative learning. Though sometime this kind of book is overwhelming to read and may not suite continues topic based reading, but for a change it does work. That's all on my list of top Hibernate books for Java programmers. With this guide, you'll master the Hibernate search to build high-performance enterprise applications.
It follows a direct and example-based approach. These clear examples will help you to grab the underlying concepts of Hibernate more efficiently. It mainly focuses on Hibernate so that you can immediately start building transaction-based engines and applications. Mastering Hibernate is a comprehensive guide that'll teach you how to use Hibernate effectively in your enterprise applications.
This book will help you to get through the day to day problems you face using Hibernate.
- Navigation menu.
- 20 Recipes for Programming MVC 3: Faster and Smarter Web Development.
- Britannica Illustrated Science Library Rocks And Minerals.
With this guide, you'll master topics such as mapping, querying, caching, and a wide range of very useful annotations. High-Performance Java Persistence. Author: Vlad Mihalcea. ISBN: X. View Book. Hibernate Tips: More than 70 solutions to common Hibernate problems. Author: Thorben Janssen.
Best Java Hibernate Books for Building ORM Applications
ISBN: Author: Cameron Wallace McKenzie. Author: James Elliott,Timothy M. O'Brien,Ryan Fowler. Java Persistence with Hibernate. Author: Madhusudhan Konda.
- How to implement equals and hashCode using the JPA entity identifier (Primary Key);
- Best books to learn Hibernate for Java developers – Blog on Java Technologies!
- Housing by people : towards autonomy in building environments;
- Szczegóły książki.
Just Hibernate is a concise, example-driven tutorial for Java beginners to learn Hibernate. It presents a short and simple introduction to Hibernate. It'll help Java developers to perform complex tasks for storing Java objects in relational databases using Hibernate. Using real-world examples, it'll walk you through Hibernate and object-relational mapping from the ground up, starting with the basics. The best thing about the book is, it'll help you gain enough knowledge and skills to start building real-world applications with Hibernate.