Just one minor update for future reference, We have to add the None
checking condition in _update_artist method as well for the update to
happen properly in the web application. But I was unable to produce the
problem in the text sqlalchemy file that I have posted in the pastebin.
@validates("artist", include_removes=True)
def _update_artist(self, key, artist, is_remove):
if artist is not None:
artist.__dict__.pop('total_sales', None)
return artist
On Tuesday, 7 August 2012 17:06:25 UTC+5:30, jeetu wrote:
>
> Just ignore the above post. I am able to get it working for adding new
> artist with albums. But I am still getting some problems while updating the
> albums's sales values from Turogears/toscawidgets2 interface. Let me bring
> the problem to sqlalchemy level then I will post it further (if the problem
> still remains). The code in the above post is working fine for adding new
> Artist and Albums. Thanks Michael for helping me out.
>
> On Tuesday, 7 August 2012 11:19:54 UTC+5:30, jeetu wrote:
>>
>> Thanks Michael for looking into my problem. I tried following your advice
>> but still not able to get the total_sale. Do I have to implement some
>> special getter/setter for memoized property. If you run the code, you will
>> see that nowhere 'print "SETTING TOTAL_SALES"' is getting executed which
>> is in the memoized definition. Also how can i access the memoized property
>> as it is not available in straight forward querying on Artist.
>>
>> http://pastebin.com/Gqa7b0dd
>>
>> On Tuesday, 7 August 2012 00:14:07 UTC+5:30, Michael Bayer wrote:
>>>
>>> @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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>>>
>>>
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