total_sales here is not a DB column here, it's just an attribute in your Python
model.
the most legit way to see "total_sales" in your SQLite database would be to
query for it. select sum(artist.sales) from artist where album_id=<some
album>.
Alternatively, a "denomalized" approach would be to copy the "total_sales"
value directly into a new column in the SQLite DB, though this is not
encouraged as it's more complicated, and allows for the database to be
inconsistent (that is, total_sales might not match the actual total_sales, if a
buggy application updated the DB incorrectly). Usually this kind of thing is
done when some particular data is needed very directly using only simple
queries for performance reasons.
On Aug 16, 2012, at 9:04 AM, jeetu wrote:
> I am not able see the total_sales column in sqlite manager plugin of firefox
> and sqlagrid of toscawidgets. But I can access the total_sales when I use
> toscawidget's dbform. Any known reasons?
>
> On Tuesday, 7 August 2012 20:56:07 UTC+5:30, jeetu wrote:
> 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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