What's the best way to count results in GQL?

Question

I figure one way to do a count is like this:

foo = db.GqlQuery(\"SELECT * FROM bar WHERE baz = \'baz\')
my_count = foo.count()

What I don\'

Answer 1

You have to flip your thinking when working with a scalable datastore like GAE to do your calculations up front. In this case that means you need to keep counters for each baz and increment them whenever you add a new bar, instead of counting at the time of display.

class CategoryCounter(db.Model):
    category = db.StringProperty()
    count = db.IntegerProperty(default=0)

then when creating a Bar object, increment the counter

def createNewBar(category_name):
  bar = Bar(...,baz=category_name)

  counter = CategoryCounter.filter('category =',category_name).get()
  if not counter:
    counter = CategoryCounter(category=category_name)
  else:
    counter.count += 1
  bar.put()
  counter.put()

db.run_in_transaction(createNewBar,'asdf')

now you have an easy way to get the count for any specific category

CategoryCounter.filter('category =',category_name).get().count