Source code for examples.dynamic_dict.dynamic_dict
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import sessionmaker
class ProxyDict:
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)
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(list(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())