On Fri, Aug 4, 2017 at 6:07 PM, Shane Carey <[email protected]> wrote:
> I am trying to remove duplicate code in this scenario described here
>
> http://docs.sqlalchemy.org/en/latest/orm/constructors.html
>
> class Obj(Base):
> def __init__(self, **kwargs):
> super().__init__(**kwargs)
> self.extra = # ... some complicated construction based off of a
> kwarg
>
> @orm.reconstructor
> def init_on_load(self):
> self.extra = # ... same complicated construction based off of self
> attribute
normally you'd factor the complexity into a new method and have
__init__ and init_on_load call that:
class Obj(Base):
def __init__(self, **kw):
self._do_complex_init(kw['foo'], kw['bar'])
@orm.reconstructor
def init_on_load(Self):
self._do_complex_init(self.foo, self.bar)
> Is it possible to intercept the setting of the attribute self.extra depends
> on
What kind of attribute (ORM mapped column? plain attribute not
linked to a SQL expression?) and then when you say "setting" do you
mean userland setting (like you said myobj.the_attribute = 5) or you
mean when it is loaded by the ORM?
Overall I think you might be interested in these events:
init -
http://docs.sqlalchemy.org/en/latest/orm/events.html?highlight=mapperevents#sqlalchemy.orm.events.InstanceEvents.init
load -
http://docs.sqlalchemy.org/en/latest/orm/events.html?highlight=mapperevents#sqlalchemy.orm.events.InstanceEvents.load
Above, the "load" event is what is used to implement
@orm.reconstructor which is from before we had a fully consistent
event system.
I'm pushing out a change in the documentation that correctly links
@orm.reconstructor to the InstanceEvents.load event.
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