02.06.2014 16:44, Michael Bayer kirjoitti:
the ORM can't persist any value for "delivery_method" unless there is
an actual attribute set event.
If you are saying session.add(DeliveryAddress()) and flushing, these
are the options for "deliveryaddress.delivery_method":
1. the value has no setting and is not present in the INSERT statement
- it gets set as NULL in the DB.
2. the value has no setting, but you have a python or server side
default set up on it. At before_insert() time, that value is still
None so that can't be what you're doing.
3. The DeliveryAddress() constructor sets delivery_method, so there's
an attribute set event.
So I can only guess that you're looking for the None here? I guess
there's some odd relationship to this Settings object such that it
already exists in the DB with some other value such that you actually
need to positively set None. In any case, to have something
happen upon DeliveryAddress(), you can either place that logic as part
of __init__() (regular Python!) or if that bothers you, you can also
set up the init() event for the DeliveryAddress class.
Settings is a singleton (just one row with ID 1). It contains the
default values for a number of things.
I will have a look at __declare_last__, thanks!
That said, sometimes I need to react to inserts and insert other rows
then. Attribute events won't help me there.
So far I've ended up making a module for these listeners and I just had
a single listener for each event (before_insert or before_flush) with a
lot of if..elif...branching.
If all of these options don't suit you and you absolutely insist on
the before_insert event, it is very easy to add to your declarative
base a mixin that sets these up for you (see
http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/declarative.html#declare-last):
class BeforeInsertMixin(object):
@classmethod
def __declare_last__(cls):
if hasattr(cls, 'before_insert'):
event.listen(cls, 'before_insert', cls.before_insert)
Base = declarative_base(cls=BeforeInsertMixin)
class DeliveryAddress(Base):
# ...
@classmethod
def before_insert(cls, mapper, connection, target):
#...
if you want to change the signature, no problem:
class BeforeInsertMixin(object):
@classmethod
def __declare_last__(cls):
if hasattr(cls, 'before_insert'):
@event.listens_for(cls, 'before_insert')
def before_insert(mapper, connection, target):
target.before_insert(object_session(target))
class DeliveryAddress(Base):
# ...
def before_insert(self, session):
#...
These are "frameworky" types of hooks that SQLAlchemy would prefer to
remain agnostic of, but it provides for you all the components you
need to create whatever system of hooks you'd like.
On Jun 2, 2014, at 8:04 AM, Alex Grönholm <alex.gronh...@nextday.fi
<mailto:alex.gronh...@nextday.fi>> wrote:
That's the first thing I tried, but validators don't get called
unless you explicitly set a value to the column.
So for something like session.add(DeliveryAddress()), the validator
doesn't get called.
maanantai, 2. kesäkuuta 2014 14.27.47 UTC+3 Michael Bayer kirjoitti:
On Jun 2, 2014, at 1:47 AM, Alex Grönholm <alex.g...@nextday.fi>
wrote:
> This has been a problem for me for years.
>
> class DeliveryAddress(Base, Address):
> ...
> delivery_method = Column(String)
> ...
>
> @event.listens_for(DeliveryAddress, 'before_insert')
> def before_insert_deliveryaddress(mapper, connection, target):
> settings = object_session(target).query(Settings).one()
> target.delivery_method = settings.default_delivery_method
>
> Is there absolutely no way to encapsulate this logic cleanly in
the actual class?
I use an attribute event for that, and more often just a simple
@validates.
@validates("default_delivery_method")
def _set_delivery_method(self, key, value):
self.settings.delivery_method = value
return value
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