mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-06-02 05:48:52 -04:00
Mike Bayer
128 lines
3.4 KiB
Python
128 lines
3.4 KiB
Python
"""A couple of helper descriptors to allow to use the same code as query
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criterion creators and as instance code. As this doesn't do advanced
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magic recompiling, you can only use basic expression-like code."""
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import new
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class MethodDescriptor(object):
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def __init__(self, func):
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self.func = func
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def __get__(self, instance, owner):
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if instance is None:
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return new.instancemethod(self.func, owner, owner.__class__)
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else:
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return new.instancemethod(self.func, instance, owner)
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class PropertyDescriptor(object):
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def __init__(self, fget, fset, fdel):
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self.fget = fget
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self.fset = fset
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self.fdel = fdel
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def __get__(self, instance, owner):
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if instance is None:
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return self.fget(owner)
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else:
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return self.fget(instance)
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def __set__(self, instance, value):
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self.fset(instance, value)
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def __delete__(self, instance):
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self.fdel(instance)
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def hybrid(func):
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return MethodDescriptor(func)
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def hybrid_property(fget, fset=None, fdel=None):
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return PropertyDescriptor(fget, fset, fdel)
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### Example code
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from sqlalchemy import *
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from sqlalchemy.orm import *
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metadata = MetaData('sqlite://')
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metadata.bind.echo = True
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print "Set up database metadata"
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interval_table1 = Table('interval1', metadata,
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Column('id', Integer, primary_key=True),
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Column('start', Integer, nullable=False),
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Column('end', Integer, nullable=False))
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interval_table2 = Table('interval2', metadata,
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Column('id', Integer, primary_key=True),
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Column('start', Integer, nullable=False),
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Column('length', Integer, nullable=False))
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metadata.create_all()
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# A base class for intervals
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class BaseInterval(object):
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@hybrid
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def contains(self,point):
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return (self.start <= point) & (point < self.end)
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@hybrid
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def intersects(self, other):
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return (self.start < other.end) & (self.end > other.start)
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def __repr__(self):
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return "%s(%s..%s)" % (self.__class__.__name__, self.start, self.end)
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# Interval stored as endpoints
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class Interval1(BaseInterval):
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def __init__(self, start, end):
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self.start = start
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self.end = end
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length = hybrid_property(lambda s: s.end - s.start)
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mapper(Interval1, interval_table1)
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# Interval stored as start and length
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class Interval2(BaseInterval):
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def __init__(self, start, length):
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self.start = start
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self.length = length
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end = hybrid_property(lambda s: s.start + s.length)
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mapper(Interval2, interval_table2)
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print "Create the data"
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session = create_session()
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intervals = [Interval1(1,4), Interval1(3,15), Interval1(11,16)]
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for interval in intervals:
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session.save(interval)
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session.save(Interval2(interval.start, interval.length))
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session.flush()
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print "Clear the cache and do some queries"
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session.clear()
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for Interval in (Interval1, Interval2):
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print "Querying using interval class %s" % Interval.__name__
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print
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print '-- length less than 10'
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print [(i, i.length) for i in session.query(Interval).filter(Interval.length < 10).all()]
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print
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print '-- contains 12'
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print session.query(Interval).filter(Interval.contains(12)).all()
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print
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print '-- intersects 2..10'
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other = Interval1(2,10)
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result = session.query(Interval).filter(Interval.intersects(other)).order_by(Interval.length).all()
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print [(interval, interval.intersects(other)) for interval in result]
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