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import datetime, os
from sqlalchemy import *
from sqlalchemy import sql
from sqlalchemy.orm import *
from sqlalchemy.ext.horizontal_shard import ShardedSession
from sqlalchemy.sql import operators
from sqlalchemy.test import *
from sqlalchemy.test.testing import eq_
from nose import SkipTest
# TODO: ShardTest can be turned into a base for further subclasses
class ShardTest(TestBase):
@classmethod
def setup_class(cls):
global db1, db2, db3, db4, weather_locations, weather_reports
try:
db1 = create_engine('sqlite:///shard1.db')
except ImportError:
raise SkipTest('Requires sqlite')
db2 = create_engine('sqlite:///shard2.db')
db3 = create_engine('sqlite:///shard3.db')
db4 = create_engine('sqlite:///shard4.db')
meta = MetaData()
ids = Table('ids', meta,
Column('nextid', Integer, nullable=False))
def id_generator(ctx):
# in reality, might want to use a separate transaction for this.
c = db1.connect()
nextid = c.execute(ids.select(for_update=True)).scalar()
c.execute(ids.update(values={ids.c.nextid : ids.c.nextid + 1}))
return nextid
weather_locations = Table("weather_locations", meta,
Column('id', Integer, primary_key=True, default=id_generator),
Column('continent', String(30), nullable=False),
Column('city', String(50), nullable=False)
)
weather_reports = Table(
'weather_reports',
meta,
Column('id', Integer, primary_key=True),
Column('location_id', Integer,
ForeignKey('weather_locations.id')),
Column('temperature', Float),
Column('report_time', DateTime,
default=datetime.datetime.now),
)
for db in (db1, db2, db3, db4):
meta.create_all(db)
db1.execute(ids.insert(), nextid=1)
cls.setup_session()
cls.setup_mappers()
@classmethod
def teardown_class(cls):
for db in (db1, db2, db3, db4):
db.connect().invalidate()
for i in range(1,5):
os.remove("shard%d.db" % i)
@classmethod
def setup_session(cls):
global create_session
shard_lookup = {
'North America': 'north_america',
'Asia': 'asia',
'Europe': 'europe',
'South America': 'south_america',
}
def shard_chooser(mapper, instance, clause=None):
if isinstance(instance, WeatherLocation):
return shard_lookup[instance.continent]
else:
return shard_chooser(mapper, instance.location)
def id_chooser(query, ident):
return ['north_america', 'asia', 'europe', 'south_america']
def query_chooser(query):
ids = []
class FindContinent(sql.ClauseVisitor):
def visit_binary(self, binary):
if binary.left.shares_lineage(
weather_locations.c.continent):
if binary.operator == operators.eq:
ids.append(shard_lookup[binary.right.value])
elif binary.operator == operators.in_op:
for bind in binary.right.clauses:
ids.append(shard_lookup[bind.value])
FindContinent().traverse(query._criterion)
if len(ids) == 0:
return ['north_america', 'asia', 'europe',
'south_america']
else:
return ids
create_session = sessionmaker(class_=ShardedSession,
autoflush=True, autocommit=False)
create_session.configure(shards={
'north_america': db1,
'asia': db2,
'europe': db3,
'south_america': db4,
}, shard_chooser=shard_chooser, id_chooser=id_chooser,
query_chooser=query_chooser)
@classmethod
def setup_mappers(cls):
global WeatherLocation, Report
class WeatherLocation(object):
def __init__(self, continent, city):
self.continent = continent
self.city = city
class Report(object):
def __init__(self, temperature):
self.temperature = temperature
mapper(WeatherLocation, weather_locations, properties={
'reports':relationship(Report, backref='location'),
'city': deferred(weather_locations.c.city),
})
mapper(Report, weather_reports)
def test_roundtrip(self):
tokyo = WeatherLocation('Asia', 'Tokyo')
newyork = WeatherLocation('North America', 'New York')
toronto = WeatherLocation('North America', 'Toronto')
london = WeatherLocation('Europe', 'London')
dublin = WeatherLocation('Europe', 'Dublin')
brasilia = WeatherLocation('South America', 'Brasila')
quito = WeatherLocation('South America', 'Quito')
tokyo.reports.append(Report(80.0))
newyork.reports.append(Report(75))
quito.reports.append(Report(85))
sess = create_session()
for c in [
tokyo,
newyork,
toronto,
london,
dublin,
brasilia,
quito,
]:
sess.add(c)
sess.commit()
tokyo.city # reload 'city' attribute on tokyo
sess.expunge_all()
eq_(db2.execute(weather_locations.select()).fetchall(), [(1,
'Asia', 'Tokyo')])
eq_(db1.execute(weather_locations.select()).fetchall(), [(2,
'North America', 'New York'), (3, 'North America', 'Toronto'
)])
eq_(sess.execute(weather_locations.select(), shard_id='asia'
).fetchall(), [(1, 'Asia', 'Tokyo')])
t = sess.query(WeatherLocation).get(tokyo.id)
eq_(t.city, tokyo.city)
eq_(t.reports[0].temperature, 80.0)
north_american_cities = \
sess.query(WeatherLocation).filter(WeatherLocation.continent
== 'North America')
eq_(set([c.city for c in north_american_cities]),
set(['New York', 'Toronto']))
asia_and_europe = \
sess.query(WeatherLocation).filter(
WeatherLocation.continent.in_(['Europe', 'Asia']))
eq_(set([c.city for c in asia_and_europe]), set(['Tokyo',
'London', 'Dublin']))
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