Re: Calculate and store the average rating
@Dave: It is not a 1-to1 as I would like each borrower to provide his own rating, and then compute the average ratings per book - to make recommendations for the highest rated books. Thanks for the example in the reply too. I will try out the SQL update shortly. @ Russ: Thanks too for the input. I will read up on signals - this is news! The denormalization - same comment as above. I'm going to try the SQL computation first, then will look at signals. The probem: I want to calculate the average rating in the BookRatings model each time an individual rating of a book is captured in the Loan model. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
Re: Calculate and store the average rating
On Sat, Dec 27, 2008 at 7:48 AM, eldonp2 <eldo...@gmail.com> wrote: > > Is there a way to calculate and store the average rating in this > example: It's not entirely clear which part of this problem you want help with. - Computing the average rating. The brute force approach would be to iterate over the relevant related objects and compute an average. A smarter approach would be to use SQL to compute the average. - Storing the average in the related model. This could be as simple as saving an instance of the BookRatings model after computing the average. You could also use signals or save() overriding to automate the update of the BookRatings model. - Model design. It's not entirely clear why you would want to denormalize the average values, and then put them into a separate model. If you provide a better description of the problem you want help with, what you have already tried, and what problems you have experienced, we may be able to provide a more meaningful answer to your problem. Yours, Russ Magee %-) --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
Re: Calculate and store the average rating
Hmm... this is slightly different... is BookRatings and Books 1 to 1?
If I store these aggregates as part of the class that it's grouping
by. Here's how I do it for restaurants:
class RestaurantRating(models.Model):
restaurant = models.ForeignKey(Restaurant)
value = models.IntegerField(null=True, blank=True)
user = models.ForeignKey(Profile)
created_at = models.DateTimeField(auto_now_add=True)
class Meta:
db_table = u'restaurant_rating'
def save(self, force_insert=False, force_update=False):
try:
super(RestaurantRating, self).save(force_insert,
force_update)
cursor = connection.cursor()
query = "SELECT count(value), avg(value) FROM
restaurant_rating WHERE restaurant_id = %s"
results = cursor.execute(query, (self.restaurant.id,))
for row in cursor.fetchall():
self.restaurant.num_ratings= row[0]
self.restaurant.average_rating = row[1]
self.restaurant.save()
except:
transaction.rollback()
else:
transaction.commit()
It's worked well for me, although I haven't used this in production
yet. Let me know if this works for you.
On Dec 26, 4:48 pm, eldonp2 <eldo...@gmail.com> wrote:
> Is there a way to calculate and store the average rating in this
> example:
>
> RATING_CHOICES = {
> '3' : 'Excellent',
> '2' : 'Good',
> '1' : 'Poor',
>
> }
>
> class Loan(
> ...
> book = models.ForeignKey(Book)
> rating = models.IntegerField(choices=RATING_CHOICES)
> ...
>
> class BookRatings(...
> ...
> book = models.ForeignKey(Book)
> rating = models.IntegerField(...here I would like the average rating
> from the Loan model...)
> nums = models.IntegerField(...and here the number of ratings
> done...)
> ...
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-users@googlegroups.com
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en
-~--~~~~--~~--~--~---
Calculate and store the average rating
Is there a way to calculate and store the average rating in this
example:
RATING_CHOICES = {
'3' : 'Excellent',
'2' : 'Good',
'1' : 'Poor',
}
class Loan(
...
book = models.ForeignKey(Book)
rating = models.IntegerField(choices=RATING_CHOICES)
...
class BookRatings(...
...
book = models.ForeignKey(Book)
rating = models.IntegerField(...here I would like the average rating
from the Loan model...)
nums = models.IntegerField(...and here the number of ratings
done...)
...
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-users@googlegroups.com
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en
-~--~~~~--~~--~--~---
