SQLAlchemy update parent when related child changes

Question

I\'m trying to model an entity that as one or more one-to-many relationships, such that it\'s last_modified attribute is updated, when

• a child is

Answer 1

Take this with a huge grain of salt, it "seems" to work, could explode:

def rel_listener(t, v, i):
    t.last_modified = now()

def listener(t, v, o, i):
    if t.config:
        t.config.last_modified = now()

from sqlalchemy import inspect

for rel in inspect(Config).relationships:
    event.listen(rel, 'append', rel_listener)
    event.listen(rel, 'remove', rel_listener)

for col in inspect(ConfigParam).column_attrs:
    event.listen(col, 'set', listener)

Problem is that the inspections make no exceptions and columns such as 'ID' and 'ConfigID' will be bound to event listeners.

Another perhaps slightly less tedious form would be to just use a list of attributes to bind events to in a similar fashion:

for attr in ['key', 'value']:
    event.listen(getattr(ConfigParam, attr), 'set', listener)

This gives you control over what is bound to events and what is not.