On Nov 29, 2011, at 2:35 PM, Łukasz Czuja wrote: > Hello, > > I'm trying to figure out a way to use Session.merge(o, load=False), on > an object which is not bound to a session (Session.remove() used after > the object was modified, but the changes were not commited). > > When the object's state is modified (instance_state(o).modified == > True) the session merge will fail with: > > "merge() with load=False option does not support objects marked as > 'dirty'. flush() all changes on mapped instances before merging with > load=False." > > So i need an rollback(o) on this object only. It might also be a good > idea to add an argument to merge() to do just that.
load=False is only a performance optimization. If you're passing it dirty objects, the optimization cannot take place and guarantee consistent data. It's not feasible for SQLAlchemy to "roll back" the attributes on an object, as it quickly gets into edge cases regarding references and collections where only the view from the relational database can really provide an accurate picture; that's why objects are fully expired, so that attributes can be refeshed from the database on access, instead of "rolled back". You'd have to figure a way to produce a clean object for merge() in the first place if you'd like to avoid its state being reconciled with that of the database. This is something that's outside the scope of what the ORM provides. If it were me I'd not be using load=False for any use case other than plain vanilla retrieval from a cache. If you want to optimize merge() for a non-caching use case, pre-load the full set of objects that you expect to pass to merge() using a series of SELECT statements, then ensure those persistent objects remain referenced. When you merge in your dirty, detached objects, the state on those objects will be reconciled with the object already in the identity map, and no SQL will be emitted. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. 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.
