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import new
class MethodDescriptor(object):
def __init__(self, func):
self.func = func
def __get__(self, instance, owner):
if instance is None:
return new.instancemethod(self.func, owner, owner.__class__)
else:
return new.instancemethod(self.func, instance, owner)
class PropertyDescriptor(object):
def __init__(self, fget, fset, fdel):
self.fget = fget
self.fset = fset
self.fdel = fdel
def __get__(self, instance, owner):
if instance is None:
return self.fget(owner)
else:
return self.fget(instance)
def __set__(self, instance, value):
self.fset(instance, value)
def __delete__(self, instance):
self.fdel(instance)
def hybrid(func):
return MethodDescriptor(func)
def hybrid_property(fget, fset=None, fdel=None):
return PropertyDescriptor(fget, fset, fdel)
### Example code
from sqlalchemy import MetaData, Table, Column, Integer
from sqlalchemy.orm import mapper, create_session
metadata = MetaData('sqlite://')
metadata.bind.echo = True
print "Set up database metadata"
interval_table1 = Table('interval1', metadata,
Column('id', Integer, primary_key=True),
Column('start', Integer, nullable=False),
Column('end', Integer, nullable=False))
interval_table2 = Table('interval2', metadata,
Column('id', Integer, primary_key=True),
Column('start', Integer, nullable=False),
Column('length', Integer, nullable=False))
metadata.create_all()
# A base class for intervals
class BaseInterval(object):
@hybrid
def contains(self,point):
return (self.start <= point) & (point < self.end)
@hybrid
def intersects(self, other):
return (self.start < other.end) & (self.end > other.start)
def __repr__(self):
return "%s(%s..%s)" % (self.__class__.__name__, self.start, self.end)
# Interval stored as endpoints
class Interval1(BaseInterval):
def __init__(self, start, end):
self.start = start
self.end = end
length = hybrid_property(lambda s: s.end - s.start)
mapper(Interval1, interval_table1)
# Interval stored as start and length
class Interval2(BaseInterval):
def __init__(self, start, length):
self.start = start
self.length = length
end = hybrid_property(lambda s: s.start + s.length)
mapper(Interval2, interval_table2)
print "Create the data"
session = create_session()
intervals = [Interval1(1,4), Interval1(3,15), Interval1(11,16)]
for interval in intervals:
session.add(interval)
session.add(Interval2(interval.start, interval.length))
session.flush()
print "Clear the cache and do some queries"
session.expunge_all()
for Interval in (Interval1, Interval2):
print "Querying using interval class %s" % Interval.__name__
print
print '-- length less than 10'
print [(i, i.length) for i in session.query(Interval).filter(Interval.length < 10).all()]
print
print '-- contains 12'
print session.query(Interval).filter(Interval.contains(12)).all()
print
print '-- intersects 2..10'
other = Interval1(2,10)
result = session.query(Interval).filter(Interval.intersects(other)).order_by(Interval.length).all()
print [(interval, interval.intersects(other)) for interval in result]
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