@memoized_property is a handy tool, and works simply, just clear out __dict__
of that key and it's reset.
since you're looking to work in python, the total sales are just:
@memoized_property
def total_sales(self):
# This should be the sum of all Album sales for this Artist. It should
# be updated as soon as/just after a new Album is added or an Album's
# sales is updated.
return sum([album.sales or 0 for album in self.albums])
the events you need are simple, just whenever "sales" or "artist" (ideally
you'd name this in the singular since it is many-to-one) change, pop the
"total_sales" out of the dict:
from sqlalchemy.orm import validates
class Album(Base):
# ...
@validates("sales")
def _update_sales(self, key, value):
if self.artist is not None:
self.artist.__dict__.pop('total_sales', None)
return value
@validates("artist", include_removes=True)
def _update_artist(self, key, artist, is_remove):
artist.__dict__.pop('total_sales', None)
return artist
On Aug 6, 2012, at 4:08 AM, jeetu wrote:
> My problem scenario is analogous to the following. I have an Artist table and
> an Album table. Each artist can have multiple albums with sales of each
> album. The artist also has a total_sales column which is basically a
> cumulative of album's sales for that artist. I tried reading about attribute
> events and memoized property but I am unable to get it integrated with my
> code. I tried to achieve something like
> https://groups.google.com/forum/?fromgroups#!topic/sqlalchemy/o_KxuHwz4WQ.
> But my lack of thorough understanding of decoraters and sqlalchemy is proving
> to be a hindrance. My example code (heavily borrowed from resources on
> internet and sqlalchemy group) is http://pastebin.com/vhRTcrWV
> Just for information if at all it matters:n my actual code I am using
> toscawidgets (inside turbogears) and dynamic forms for creating Albums
> table's values and Artist's values on a single page.
>
> PS: I hope it is not sounding like homework
>
>
>
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