Source code for examples.custom_attributes.listen_for_events
"""Illustrates how to attach events to all instrumented attributes
and listen for change events.
"""
from sqlalchemy import event
def configure_listener(class_, key, inst):
def append(instance, value, initiator):
instance.receive_change_event("append", key, value, None)
def remove(instance, value, initiator):
instance.receive_change_event("remove", key, value, None)
def set_(instance, value, oldvalue, initiator):
instance.receive_change_event("set", key, value, oldvalue)
event.listen(inst, "append", append)
event.listen(inst, "remove", remove)
event.listen(inst, "set", set_)
if __name__ == "__main__":
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
class Base(object):
def receive_change_event(self, verb, key, value, oldvalue):
s = "Value '%s' %s on attribute '%s', " % (value, verb, key)
if oldvalue:
s += "which replaced the value '%s', " % oldvalue
s += "on object %s" % self
print(s)
Base = declarative_base(cls=Base)
event.listen(Base, "attribute_instrument", configure_listener)
class MyMappedClass(Base):
__tablename__ = "mytable"
id = Column(Integer, primary_key=True)
data = Column(String(50))
related_id = Column(Integer, ForeignKey("related.id"))
related = relationship("Related", backref="mapped")
def __str__(self):
return "MyMappedClass(data=%r)" % self.data
class Related(Base):
__tablename__ = "related"
id = Column(Integer, primary_key=True)
data = Column(String(50))
def __str__(self):
return "Related(data=%r)" % self.data
# classes are instrumented. Demonstrate the events !
m1 = MyMappedClass(data="m1", related=Related(data="r1"))
m1.data = "m1mod"
m1.related.mapped.append(MyMappedClass(data="m2"))
del m1.data