mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-06-04 06:48:27 -04:00
Mike Bayer
84 lines
2.5 KiB
Python
84 lines
2.5 KiB
Python
"""Illustrates how to place a dictionary-like facade on top of a dynamic_loader, so
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that dictionary operations (assuming simple string keys) can operate upon a large
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collection without loading the full collection at once.
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This is something that may eventually be added as a feature to dynamic_loader() itself.
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Similar approaches could be taken towards sets and dictionaries with non-string keys
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although the hash policy of the members would need to be distilled into a filter() criterion.
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"""
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class MyProxyDict(object):
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def __init__(self, parent, collection_name, childclass, keyname):
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self.parent = parent
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self.collection_name = collection_name
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self.childclass = childclass
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self.keyname = keyname
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def collection(self):
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return getattr(self.parent, self.collection_name)
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collection = property(collection)
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def keys(self):
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descriptor = getattr(self.childclass, self.keyname)
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return [x[0] for x in self.collection.values(descriptor)]
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def __getitem__(self, key):
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x = self.collection.filter_by(**{self.keyname:key}).first()
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if x:
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return x
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else:
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raise KeyError(key)
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def __setitem__(self, key, value):
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try:
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existing = self[key]
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self.collection.remove(existing)
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except KeyError:
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pass
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self.collection.append(value)
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from sqlalchemy.ext.declarative import declarative_base
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from sqlalchemy import *
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from sqlalchemy.orm import *
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Base = declarative_base(engine=create_engine('sqlite://'))
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class MyParent(Base):
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__tablename__ = 'parent'
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id = Column(Integer, primary_key=True)
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name = Column(String(50))
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_collection = dynamic_loader("MyChild", cascade="all, delete-orphan")
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def child_map(self):
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return MyProxyDict(self, '_collection', MyChild, 'key')
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child_map = property(child_map)
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class MyChild(Base):
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__tablename__ = 'child'
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id = Column(Integer, primary_key=True)
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key = Column(String(50))
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parent_id = Column(Integer, ForeignKey('parent.id'))
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Base.metadata.create_all()
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sess = sessionmaker()()
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p1 = MyParent(name='p1')
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sess.add(p1)
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p1.child_map['k1'] = k1 = MyChild(key='k1')
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p1.child_map['k2'] = k2 = MyChild(key='k2')
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assert p1.child_map.keys() == ['k1', 'k2']
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assert p1.child_map['k1'] is k1
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p1.child_map['k2'] = k2b = MyChild(key='k2')
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assert p1.child_map['k2'] is k2b
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assert sess.query(MyChild).all() == [k1, k2b]
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