Hi Wilson,
You outlined the pattern to do this yourself. Fetch the entities
you want to average, add up the ratings, then divide by the number of
ratings. There are several ways to do this, in Python one very easy
to follow method might look like:
# Get the ratings entities.
ratings_entities = Ratings.all().fetch(100)
total_rating = 0.0
ratings_count = 0
for entity in ratings_entities:
total_rating += entity.rating
ratings_count += 1
average_rating = total_rating / ratings_count
# Or, more concisely
ratings = [entity.rating for entity in ratings_entities]
average_rating = float(sum(ratings)) / count(ratings)
However, note that you should *not* do this on every request. Your
app will perform terribly. Instead you should come up with a way to
compute and store the computed average rating. You could do this when
someone adds a rating, or periodically update the average. you'll
have to decide which method makes the most sense for you.
Robert
On Wed, May 4, 2011 at 02:52, Wilson Giese <giese.wil...@gmail.com> wrote:
> I'm pretty new to databases and googles app engine, and I'm having a
> hard time getting saved data and averaging it. So basically we have a
> comments and ratings system where they can type comments and add
> ratings, but I can't figure out how to get all the ratings, and
> average them. I just simply do not know how to do it.
>
> Is there any way I can pull saved data and average?
>
> So say "rating" is in database, and there were 5 ratings currently.
> How would I get all ratings, add them together, and divide by the
> number of ratings. Is this even possible?
>
> Sorry if this is confusing.
>
> - Thanks in advance
>
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