[xwiki-devs] [proposal] Add TransactionProvider to xwiki-store so FS attachment store can synchronize with main-store without caring what the main store is.

We need a way for subservient stores such as FS attachments to get transactions from the main store so that it can know to rollback if there is an error in the main store. In order to Cloud/DataNucleus store plug in seamlessly and function with FS attachments, FS attachments needs to be able to get transactions from the main store without knowing or caring what that main store is. I propose this: Add a new storage submodule: xwiki-platform-store-transactionprovider which provides this interface which extends javax.inject.Provider: @ComponentRole public interface XWikiTransactionProvider extends Provider<StartableTransactionRunnable<? extends XWikiTransaction>> { // No additional functions, just the get() from Provider. } The default implementation for now will be a wrapper which picks out the real TransactionProvider based on what the main store is, as defined in xwiki.cfg. This will allow code to get a transaction from the main store then get TransactionRunnables from the main store and use them with this transaction and be assured that you won't be using a Hibernate TransactionRunnable with a Cassandra Transaction. WDYT? Caleb