On Oct 23, 2013, at 8:06 PM, Daniel Grace <thisgenericn...@gmail.com> wrote:
> I have a situation where an object in the ORM performs some calculations and > other assorted checks. One of these situations is checking to see the > difference between the original value of an attribute and the current value > -- in particular, some of the validation going on should prohibit a change > that causes a particular check to fail, but only if that check wasn't already > failing (e.g. some legacy) > > I see that I can use inspect() to get the history of attributes, but that > quickly gets unwieldy when working with a large number of attributes. What > I'd love to be able to do is something like: > > def do_something(self): > orig = get_original_version(self) > delta = self.value - orig.value > # .... > > Is there a simple way to accomplish this? Right now I'm doing something like: > > orig_value, = inspect(self).attrs.value.history.non_added or (default_value, ) > > which seems messy and only works for scalar values. a phrase like “unwieldy with a large number of attributes” doesn’t make sense to me, is this a collection of attributes in a list or something, in which case iterate through that list and call getattr(attrs, attrname).history? if an API is verbose, just put a function around it that does what you need. if as implied in the subject that some side effect is occurring that’s causing a flush to occur hence “losing changes”, probably run your operations within a session.no_autoflush: block (http://docs.sqlalchemy.org/en/rel_0_8/orm/session.html?highlight=no_autoflush#sqlalchemy.orm.session.Session.no_autoflush). history works for collections as well. this is the fine grained API to get at attribute history before a flush and attrs supports iteration through all available attributes, so just use a loop like this: def delta(obj): d = {} for attr in inspect(obj).attrs: if attr.history.has_changes(): d[attr.key] = attr.history.added, attr.history.deleted return d im not sure what exactly you’d like to see for collections, the above will just put a tuple of (things added), (things removed) for that entry in the dictionary. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out.
