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class ProxyDict(object):
def __init__(self, parent, collection_name, childclass, keyname):
self.parent = parent
self.collection_name = collection_name
self.childclass = childclass
self.keyname = keyname
@property
def collection(self):
return getattr(self.parent, self.collection_name)
def keys(self):
descriptor = getattr(self.childclass, self.keyname)
return [x[0] for x in self.collection.values(descriptor)]
def __getitem__(self, key):
x = self.collection.filter_by(**{self.keyname:key}).first()
if x:
return x
else:
raise KeyError(key)
def __setitem__(self, key, value):
try:
existing = self[key]
self.collection.remove(existing)
except KeyError:
pass
self.collection.append(value)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship
engine=create_engine('sqlite://', echo=True)
Base = declarative_base(engine)
class Parent(Base):
__tablename__ = 'parent'
id = Column(Integer, primary_key=True)
name = Column(String(50))
_collection = relationship("Child", lazy="dynamic", cascade="all, delete-orphan")
@property
def child_map(self):
return ProxyDict(self, '_collection', Child, 'key')
class Child(Base):
__tablename__ = 'child'
id = Column(Integer, primary_key=True)
key = Column(String(50))
parent_id = Column(Integer, ForeignKey('parent.id'))
def __repr__(self):
return "Child(key=%r)" % self.key
Base.metadata.create_all()
sess = sessionmaker()()
p1 = Parent(name='p1')
sess.add(p1)
print "\n---------begin setting nodes, autoflush occurs\n"
p1.child_map['k1'] = Child(key='k1')
p1.child_map['k2'] = Child(key='k2')
# this will autoflush the current map.
# ['k1', 'k2']
print "\n---------print keys - flushes first\n"
print p1.child_map.keys()
# k1
print "\n---------print 'k1' node\n"
print p1.child_map['k1']
print "\n---------update 'k2' node - must find existing, and replace\n"
p1.child_map['k2'] = Child(key='k2')
print "\n---------print 'k2' key - flushes first\n"
# k2
print p1.child_map['k2']
print "\n---------print all child nodes\n"
# [k1, k2b]
print sess.query(Child).all()
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