Wednesday 8 July 2009

Hibernate and JPA

I've been posting responses to various queries on the Hibernate Forums lately.

There seem to be a few recurring queries, so I'm looking to put together a white paper of sorts.

Here are my thoughts of what this might include.

JPA versus Hibernate:
- Standards compliant versus proprietary
- EntityManager versus Session

JPA does not require EJB3
- using a JPA implementation does not necessarily require an EJB3 container

JPA implementations:
- Hibernate
- DataNucleus (formerly known as JPox)
- Eclipselink
- OpenJPA
- Toplink
- ...?

Things to consider when evaluating products for your product or project:
- Licensing
- Stability
- Documentation and support
- Performance
- Benchmarking that matches your system's likely use cases
- Cost

JDBC Connection pooling
- Avoiding stale connections
- Implementations:
- c3p0
- Spring / Tomcat
- ...?

Lazy initialisation
- collections


XML versus Annotation based configuration

- Annotations for declaring Transactional behaviour of methods
- Which methods in which classes to mark with transactional annotation

- Second level cache
- Query cache
- Session / EntityManager

Performance issues
- N+1 queries
- batch size

Coding considerations:
- lazy initialisation exceptions
- avoid use of instanceof operator when proxies may be in place

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