On Jul 14, 4:56 am, sacabuche <sacabu...@gmail.com> wrote: > In fact i was only querying, but when i add many items in the same > flush, all items(of same category)get the same value, and i don't know > how to include the sku number already calculated to the query, that's > the reason because i tried this approach of saving "last_sku_value", > but i sow that something was really bad. > > I tried to execute the query on __init__() of my class but i had to > pass the session to my object or take my session from a global so i > thought it was a bad idea. > > And i could create my object add it to my session and after call a > function "class.new_sku()", but i dislike the idea to rewrite this for > each item. > > this is my "get_last_value()" code, maybe it'll be clear: > > def get_last_value(self, session, cls, instance): > """execute a query to find the last value""" > try: > return self.last_value[instance.dynamic.value] > except KeyError: > self.last_value_key = "%s-%s" %(instance.dynamic.static, > instance.dynamic.value) > > last_sku_value = session.query(cls.value)\ > .filter(cls.dynamic == instance.dynamic)\ > .order_by(desc(cls.date_insert)).first() > > if not last_sku_value: > return None > try: > return last_sku_value[0] > except IndexError: > return None
your options for doing a query in order to get some database related information when you make a new object are: 1. use a scoped_session, so that a global transaction is available, and do it in __nit__. Usually any app I write of any importance will be using this technique, and issues like these are not a problem. 2. after session attach, using SessionExtension.after_attach, using the given Session 3. before an insert, using MapperExtension.before_insert, using the Connection passed to that method 4. before flush, using SessionExtension.before_flush 5. as a default value on the column, using the "default" callable of Column, you can pass either a SQL expression that will execute (see http://www.sqlalchemy.org/docs/metadata.html#sql-expressions ), or a callable that accepts a "context" argument (this is a little more exotic, let me know if you want to try that, a plain SQL expression is probably all you need here though) > > On 13 jul, 16:35, Michael Bayer <mike...@zzzcomputing.com> wrote: > > > On Jul 13, 2010, at 10:21 AM, sacabuche wrote: > > > > I was trying to get the last value "before_insert" a new item but i > > > didn't find out, so i change of strategy and i saved the last value of > > > this method, but the problem is that when i do other commits my old > > > MapperExtension attribute (self.last_value) get the last value and i > > > dislike it, even when I close and open a new Session (discovered in my > > > tests) > > > > This is my code: > > > > class _ValueExtension(MapperExtension): > > > """Set new value for SkuDynamic and SKuUnique""" > > > def __init__(self): > > > self.last_value = {} # <<--- THE PROBLEM > > > self.first_value = FIRST_VALUE > > > > def before_insert(self, mapper, connection, instance): > > > session = object_session(instance) > > > cls = instance.__class__ > > > > last_sku_value = self.get_last_value(session, cls, instance) > > > > if not last_sku_value: > > > instance.value = self.first_value > > > else: > > > instance.value = next_value(last_sku_value) > > > > self.last_value[self.last_value_key] = instance.value > > > self.set_values(instance) > > > > #def after_insert(self, mapper, connection, instance): > > > # self.__init__() #<--- IF I DO THIS I DON'T HAVE THE LAST > > > VALUE IN THE SAME FLUSH > > > > #def after_update(self, mapper, connection, instance): > > > # self.__init__() > > > > def get_last_value(self, session, cls, instance): > > > """This have to return just one value > > > and set self.last_value_key is nedded to update elements in same > > > session > > > Execute The Query or check self.last_value > > > """ > > > raise NotImplementedError, 'implement this function' > > > > def set_values(self, instance): > > > """Use if necesary""" > > > pass > > > A MapperExtension is persistent for the life of the application and also is > > accessed concurrently, so it is not an appropriate place to store a count > > for things things that are local to a specific flush, and its really not a > > good place in general to do what you're trying to do (though its not clear > > above what you're trying to accomplish, if you want a global "last sku" or > > a "sku" specific to one flush). > > > You'd be better off querying the database for the "last sku value" when you > > need it, or just adding code to your classes __init__() method to keep > > track of sku numbers in memory as needed. > > > > Thanks > > > > -- > > > You received this message because you are subscribed to the Google Groups > > > "sqlalchemy" group. > > > To post to this group, send email to sqlalch...@googlegroups.com. > > > To unsubscribe from this group, send email to > > > sqlalchemy+unsubscr...@googlegroups.com. > > > For more options, visit this group > > > athttp://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@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.
