join()/merge() helper functions/classes

[dw]

Once Key creation (issue #23) and iteration (#37) are made cheap, implementing some less trivial query styles becomes interesting. Not decided on what this should look like. Maybe:

class User(acid.meta.Model):
    name = acid.meta.String()
    location = acid.meta.String()
    age = acid.emta.Integer()

    @acid.meta.index
    def by_location(self):
        return self.location

    @acid.meta.index
    def by_age(self):
        return self.age


# Find everyone in London aged 29-33.
join = acid.Join()
join.intersect(User.by_age, lo=29, hi=33, include=True)
join.intersect(User.by_location, args="London")
join.order(User.by_age)

for user in join:
    print 'Found', user

[dw]

Perhaps an interface like:

# Return a Merge instance representing keys of all users interested
# in swimming or snorkling. 
lifestyles = acid.merge(User.by_lifestyle.exact('swimming'),
                        User.by_lifestyle.exact('snorkling'))

# Return a Join instance representing keys of all users present in
# `lifestyles', and additionally female and aged 16-32.
population = acid.join(User.by_age.range(16, 32),
                       User.by_sex.exact('male'),
                       lifestyles)

print('There are %d males 16-32 who enjoy swimming or snorkling' %\
      population.count())

How to represent non-indexed criteria?