Hello,
I've implemented a 'read' event for attributes, similar to 'set'. It's
called 'read' and not 'get' because it's fired only when data is fetched
from the database.
The implementation looks a bit crude to me, as I'm not so familiar with
sqlalchemy internals. (but this exercise did teach a lot)
What do you think about it? I can write tests if you think this can be
included in the mainline.
Best regards,
Burak
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diff -r 3654d6a30454 lib/sqlalchemy/orm/events.py
--- a/lib/sqlalchemy/orm/events.py Tue Jul 05 19:33:05 2011 -0400
+++ b/lib/sqlalchemy/orm/events.py Wed Jul 06 14:02:00 2011 +0300
@@ -1044,3 +1044,20 @@
"""
+ def read(self, target, value, old, initiator):
+ """Receive a scalar read event.
+
+ :param target: the object instance receiving the event.
+ If the listener is registered with ``raw=True``, this will
+ be the :class:`.InstanceState` object.
+ :param value: the value being set. If this listener
+ is registered with ``retval=True``, the listener
+ function must return this value, or a new value which
+ replaces it.
+ :param oldvalue: the previous value being replaced. This
+ may also be the symbol ``NEVER_SET`` or ``NO_VALUE``.
+ :param initiator: the attribute implementation object
+ which initiated this event.
+ :return: if the event was registered with ``retval=True``,
+ the given value, or a new effective value, should be returned.
+ """
diff -r 3654d6a30454 lib/sqlalchemy/orm/strategies.py
--- a/lib/sqlalchemy/orm/strategies.py Tue Jul 05 19:33:05 2011 -0400
+++ b/lib/sqlalchemy/orm/strategies.py Wed Jul 06 14:02:00 2011 +0300
@@ -147,7 +147,15 @@
col = adapter.columns[col]
if col is not None and col in row:
def new_execute(state, dict_, row):
- dict_[key] = row[col]
+ value = row[col]
+ old = dict_.get(self.key, util.symbol('NO_VALUE'))
+
+ attr = getattr(self.parent_property.parent.class_, key)
+ impl = attr.impl
+ for fn in impl.dispatch.read:
+ value = fn(state, value, old, impl)
+
+ dict_[key] = value
return new_execute, None, None
else:
def new_execute(state, dict_, row):
