example.py

import sqlalchemy
import waffle

engines = [
        sqlalchemy.create_engine('sqlite:///:memory:'), 
        sqlalchemy.create_engine('sqlite:///:memory:'), 
]

def to_users(record):
    yield {'user_id': record.value['user_id']}

def to_days(record):
    yield {'day': record.value['day']}

event_user_idx = waffle.Index('event_user', 
        columns=[sqlalchemy.Column('user_id', waffle.UUIDColumn)], 
        shard=waffle.ShardByPrimaryKey(engines), 
        mapper=to_users)

event_day_idx = waffle.Index('event_day', 
        columns=[sqlalchemy.Column('day', sqlalchemy.String(length=16))], 
        shard=waffle.ShardByPrimaryKey(engines),
        mapper=to_days)

events = waffle.Entity('event', engines=engines, indices=[event_user_idx, event_day_idx], compress=True)

events.create()

users = waffle.Entity('user', engines=engines)
users.create()

user = users.new() 
event = events.new()
event.value = {
    'title': 'My Awesome event',
    'user_id': user.id,
    'day': 'monday',
    } 

# Save the event
events.save(event)

# Save the user
users.save(user)

# Load the event by user id:
result = events.select(event_user_idx.c.user_id == user.id)
print result[0]