Almost every Java developer knows ORM concepts and Hibernate as the most popular solution in Java world in this area. But it is big surprise that very small percent of Java developers (even experienced ones) can answer very simple questions about how Hibernate really do all this “magic”. In this live coding session we will go through many practical samples and finally show truth to the Java community. ;) P.S. After this talk you could pass through any Senior Developer interview easily. Code samples can be found here: https://github.com/xpinjection/hibernate-basics .

1. Hibernate, how the magic
is really done?
Mikalai Alimenkou/Igor Dmitriev
http://xpinjection.com
@xpinjection

5. Disclaimer
This is only my
personal experience

6. You could follow code samples
https://github.com/xpinjection/hibernate-basics

7. What Hibernate really does?

8. PURE MAGIC!

9. Demo database schema

10. #1. Lazy loading internals
• Persistent collections
• Lazy component/field
• Entity VS Proxy

12. #2. WHAT?!? Proxies?
• Load
• Optimized dirty checking
• Lazy loading

14. #3. What about collections?
• Collections affect performance
• All relations are lazy by default
• Some works not like you expect
• Merging values is always a pain
• Extra laziness is available

16. #4. But what was changed?
• Dirty checking is applied:
– Default approach based on
properties with reflection
– Optimized with bytecode
instrumentation
– Manual with
SelfDirtyCheckingEntity

18. #5. But when real queries run?
• Predefined order of queries is applied
– inserts
– updates
– deletions of collections elements
– inserts of the collection elements
– deletes
• Flush mode AUTO tries to be “smart”

21. @xpinjection
http://xpinjection.com
mikalai.alimenkou@xpinjection.com
ihor.dmitriiev@gmail.com