Unlike most of the SQLAlchemy caching examples, I'm not using query-level caching but rather caching at the instance / object level. I'm using the ORM and I have a SQLAlchemy object that I load and occasionally store in a second level cache. I have a custom 'get' loading function that checks the second level cache based on primary key and returns the cached copy if present and populates the cache if not.
I also have an event handler on 'after_commit' that checks the session for dirty objects that are cached (with a simple class property of __cached__=True) and does either an invalidate or write-back to the cache when these objects are dirty and cached. This pattern is pretty simple and works great. My problem is that I'd like to be able to use this same (or similar) pattern for more complex SQLAlchemy objects containing relationships. I'd like the cache to contain not only the 'base' object but all (lazy) loaded related obejcts. I have no problem storing and retrieving these objects (and relationships) from the cache, my problem comes from the invalidation/write-back part. Lets say I have object A that's in the cache and it has a relationship, A.B that was stored along with it in the cache. If I retrieve A from the cache I can get A.B and I get the cached copy of B. If B is modified, however, then my simple cache invalidator event handler doesn't see that B is cached (no __cached__ property on B) and B gets committed to the database without the cached copy of A being invalidated. Now subsequent cache hits of A will have a stale A.B relationship. So my question is, is there a clean / simple way to mark A for invalidation when B is modified? I've come up with a few schemes but all of them seem brittle, complicated, and my intuition is telling me that I'm reinventing the wheel; that some facility in SQLAlchemy itself may be useful in walking this relationship graph to find loaded, connected relationships who's cached represenations might need to be invalidated. Alternatively, is there another pattern that would be better suited to this kind of object-level caching? Thanks! -Mike -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To view this discussion on the web visit https://groups.google.com/d/msg/sqlalchemy/-/FdvwpzOlOX8J. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
