How to handle several DB schemas with Hibernate?

Question

In one of my projects, I have an application that manages several clients (or customer if you prefer). For each of them, I have a dedicated schema on a database. However, th

Answer 1

If only one at a time will every be required, it makes it much simpler. Simply create a SessionFactory per database. Avoid the HibernateUtils static SessionFactory instance approach and you won't have any problems.

A neat way to do this with Spring if you don't have too many databases (hundreds) is to instantiate a separate Spring ApplicationContext for each one that contains the SessionFactoryBean and DataSource configurations specially for that database.

You can use Spring mechanisms like PropertyOverrideConfigurer and a common parent ApplicationContext to factor out all the common stuff so that your many child ApplicationContexts are small and maintainable.

Then when a request comes in, just select the ApplicationContext you want to work with and start pulling beans out of it.

If you want to do it without Spring, you could also create multiple SessionFactory instances and store the "current" one in a static ThreadLocal.

Answer 2

Unfortunately, the Real World often does require multiple databases/schemas, especially when you have a vendor product whose database must be distinct from your corporate databases.

Making an arbitrary number of databases would be a mess, and for that, you really SHOULD consider a better form of data organization. But for a fixed (hopefully small) set of databases, just define them in the persistence configuration with a separate PersistenceUnit for each (which implies a separate EntityManager).

Using your illustrated inheritance scheme, you would assign the appropriate EntityManager to each derived class, assuming that the framework lets you.