Hello there, I am evaluating Cayenne for use in a new project. I have read the documentation and experimented a bit but I'm left with a few questions. I hope I can get some answers here ;-)
1. When Cayenne accesses the database, are PreparedStatements used (and cached) within a single DataContext? That is: if code causes 100x the same SQL to be generated and executed (select xxx from yyy where id=?) is this prepare once, cached and only executed multiple time or is it fully created every time? 2. When Cayenne executes updates does it update the entire record or does it only update the fields that changed? If it's the latter case: can it be disabled to always update the full record (to allow for statement caching - if available)? 3. The documentation states that when you call rollbackChanges() a transaction the DataContext state is restored to the state it had before. Does it do this by using "copies" of the objects it has read or is the database re-queried? 4. What happens if data gets commited to the database and a SQLException occurs (like "duplicate key", "null in non-null column" etc? Specifically: 4.a Is the state of the DataContext once such an error occurs still usable? 4.b Are the values of a persistent object in that DataContext changed during the commit or rolled back to some earlier state? 4.c Would it be possible to "fix" the values on just the objects that "failed" in the same context and commit again? 5. When using "nested" DataContext, if you commit to the "upper" DataContext I expect that the changes are only propagated to the Object Store in that upper context, not to the database. Is that correct? 6. The current implementation uses generated base classes to contain Cayenne-specific code. JPA implementations need something like bytecode-generation (proxies) to add code to persistent classes as JPA-defined classes need no platform-specific base class. So I assume that the JPA variant of Cayenne will have something like that. Are there plans to extend this to the Cayenne-specific interface? I would not want to use JPA because it sucks bigtime, but having clean classes is a wish. 7. The project is currently busy supporting the JPA standard. Is it the vision of this project to become a JPA provider mainly and deprecate the own interfaces? If Cayenne would become a JPA implementation only it would not be the correct choice for my project since that standard is a lousy one. 8. If I would select Cayenne for my project I would need to add some features to it. The reason is that I will access an already-existing legacy database with lots of oddities like triggers and stuff. Specifically: a. I would need to add an alternative version of "Optimistic locking" where a specific field in the database would hold a timestamp or version number. This number should be maintained by Cayenne i.e. incremented as soon as Cayenne inserts/updates the record. It would also be used in the where for updates/deletes exactly like the current optimistic locking mechanism to check for changes at that time. This also has another consequence (8.c) b. I would need support for database-generated fields at update and insert time. I must be able to mark fields as "generated at update, generated at insert or both". Cayenne should retrieve these fields after inserting/updating a record to keep the Object representation in-sync with the database. For some databases this would require a "select after update"; other databases (Oracle, Postgresql) can return the changed fields in the same statement (insert xxxx returning yyy). This also requires 8.c: c. Both these changes require that all generated fields get copied and stored within a database commit so that the original values (before the commit) can be restored when flushing data to the database fails; this is needed to keep the DataContext consistent after a commit failure. Are these extensions doable without rewriting the entire implementation;-)? Would these changes be acceptable to be incorporated in Cayenne? Lots of questions,I know.. I hope someone can find some time to help me by answering them!!! Thanks in advance for your time, Frits Jalvingh
