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"""Illustrates customized class instrumentation, using
the :mod:`sqlalchemy.ext.instrumentation` extension package.
In this example, mapped classes are modified to
store their state in a dictionary attached to an attribute
named "_goofy_dict", instead of using __dict__.
this example illustrates how to replace SQLAlchemy's class
descriptors with a user-defined system.
"""
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy import MetaData
from sqlalchemy import Table
from sqlalchemy import Text
from sqlalchemy.ext.instrumentation import InstrumentationManager
from sqlalchemy.orm import registry as _reg
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
from sqlalchemy.orm.attributes import del_attribute
from sqlalchemy.orm.attributes import get_attribute
from sqlalchemy.orm.attributes import set_attribute
from sqlalchemy.orm.instrumentation import is_instrumented
registry = _reg()
class MyClassState(InstrumentationManager):
def get_instance_dict(self, class_, instance):
return instance._goofy_dict
def initialize_instance_dict(self, class_, instance):
instance.__dict__["_goofy_dict"] = {}
def install_state(self, class_, instance, state):
instance.__dict__["_goofy_dict"]["state"] = state
def state_getter(self, class_):
def find(instance):
return instance.__dict__["_goofy_dict"]["state"]
return find
class MyClass:
__sa_instrumentation_manager__ = MyClassState
def __init__(self, **kwargs):
for k in kwargs:
setattr(self, k, kwargs[k])
def __getattr__(self, key):
if is_instrumented(self, key):
return get_attribute(self, key)
else:
try:
return self._goofy_dict[key]
except KeyError:
raise AttributeError(key)
def __setattr__(self, key, value):
if is_instrumented(self, key):
set_attribute(self, key, value)
else:
self._goofy_dict[key] = value
def __delattr__(self, key):
if is_instrumented(self, key):
del_attribute(self, key)
else:
del self._goofy_dict[key]
if __name__ == "__main__":
engine = create_engine("sqlite://")
meta = MetaData()
table1 = Table(
"table1",
meta,
Column("id", Integer, primary_key=True),
Column("name", Text),
)
table2 = Table(
"table2",
meta,
Column("id", Integer, primary_key=True),
Column("name", Text),
Column("t1id", Integer, ForeignKey("table1.id")),
)
meta.create_all(engine)
class A(MyClass):
pass
class B(MyClass):
pass
registry.map_imperatively(A, table1, properties={"bs": relationship(B)})
registry.map_imperatively(B, table2)
a1 = A(name="a1", bs=[B(name="b1"), B(name="b2")])
assert a1.name == "a1"
assert a1.bs[0].name == "b1"
sess = Session(engine)
sess.add(a1)
sess.commit()
a1 = sess.query(A).get(a1.id)
assert a1.name == "a1"
assert a1.bs[0].name == "b1"
a1.bs.remove(a1.bs[0])
sess.commit()
a1 = sess.query(A).get(a1.id)
assert len(a1.bs) == 1
|
