Hi all,
We are implementing a custom ConnectionProvider implementation for supporting multidatabase multitenancy (we are using hibernate 4.2.x in OSGi environment).
Our custom ConnectionProvider is mysql datasource based.
We are wondering what is the best implementation for the methods isUnwrappableAs and unwrap. We are looking at some of the OOB implementations included in Hibernate distribution but we are quite confused:

- The single tenant datasource-based connection provider like org.hibernate.service.jdbc.connections.internal.DatasourceConnectionProviderImpl allows the unwrapping of the DataSource.

- However a multitenant datasource-based implementation like org.hibernate.service.jdbc.connections.spi.DataSourceBasedMultiTenantConnectionProviderImpl only allows the unwrapping of MultiTenantConnectionProvider and AbstractMultiTenantConnectionProvider.

The javadoc of org.hibernate.service.spi.Wrapped interface (the one defining the methods isUnwrappableAs and unwrap) states: "Optional contract for services that wrap stuff that to which it is useful to have access. For example, a service that maintains a javax.sql.DataSource might want to expose access to the javax.sql.DataSource or its java.sql.Connection instances"

Could our hibernate gurus explain us what are the best implementation for these two methods?

Thanks in advance

That's because the DatasourceConnectionProviderImpl wraps a single DataSource so we know to which dataSource to unwrap.



For a multitenant environment where you have multiple DataSources, which one do you think we could choose if we decide to unwrap to a DataSource? remamber that this method does not take a tenant identifier.



I tried to find where these two methods are used, and couldn't find any specific place where they are needed. Do you have any specific issue related to them? Otherwise, just use the AbstractMultiTenantConnectionProvider logic.

Thanks for the very quick response!



We could use a threadlocal variable in order to track the current tenant. Before unwrapping the datasource we could get the current tenant value from the threadlocal var. Could it make sense?



Not at the moment :-), we are just wondering (like you) if there are any external frameworks or other hibernate's pieces of code that need these methods. The only piece of code we found is class org.springframework.orm.hibernate3.SessionFactoryUtils that is deprecated.

Our question is whether Wrapped methods are really used anywhere :-)

That could work, indeed.



I'm not aware of any particular framework or use case that depends on these two methods. One option is to just throw UnsupportedOperationException and think about the best way to implement them once you have an actual use case from a client and have more context on the problem.