On Dec 4, 2009, at 2:20 PM, Alessandro Dentella wrote:
> On Fri, Dec 04, 2009 at 01:27:46PM -0500, Michael Bayer wrote:
>>
>> On Dec 4, 2009, at 1:18 PM, Alessandro Dentella wrote:
>>
>>>>> Is the only solution to attach an instance (u.job = myjob) or is there
>>>>> another solution that doesn't require me to build the instance?
>>>>
>>>> if you want SQLA's delete-orphan capability, that's the only way. If you
>>>> want to rely upon CASCADE rules in your DB to handle it instead, that's
>>>> another way to go.
>>>
>>> thanks, and really... managing in the db is such a simple thing...
>>>
>>> Is there a why to find out the related class (that one u.job should be
>>> instance of) so that I can issue a query on that?
>>
>>
>> err, given what to start with ?
>
> ops. Let's say starting from the class and the instance.
>
> class Project(Base):
> __tablename__ = "project"
> id = Column(Integer, primary_key=True)
> name = Column(String(30), nullable=False)
>
> class Delivery(Base):
> __tablename__ = 'delivery'
> id = Column(Integer, primary_key=True)
> project_id = Column(ForeignKey(Project.id), nullable=False)
>
> project = orm.relation('Project', backref=orm.backref('deliveries',
> cascade="all, delete-orphan", lazy=False))
>
>
> sess = session()
> p = Project()
> d = Delivery()
> d.project_id = p.id
>
> # now I want to create automatically the instance 'p' having just
>
> * the value 'p.id'
> * d
> * the name of the attribute (that is a ForeignKey) project_id
well what you'd need here is the name "project", pull that attribute off of d's
mapper and figure it out from there. you see this is why SQLA doesn't know
what to do with your "d.project_id" and why we don't get into attaching rules
to foreign key identifiers. Its only a target during the flush, and a value
inside a SQL expression that is populated during a lazy load. it could just
as well be associated with multiple relations() attached to your Delivery
class, and if the mapping is really exotic those relations could even be
loading different classes based on the same column attribute - it can be in any
number of primaryjoin expressions for example.
So if you really only had "project_id", and you want to assume its only used in
one relation() on d, this is what you'd have to do:
# get parent mapper
mapper = object_mapper(d)
# convert from attribute to actual column
column = mapper.get_property('project_id').columns[0]
# search through all properties
for prop in mapper.iterate_properties:
# search through "local=remote" pairs for that prop (usually just one tuple)
if hasattr(prop, 'local_remote_pairs'):
for local, remote in prop.local_remote_pairs:
if local is column:
result = remote
break
else:
result = None
if result is not None:
target_class = prop.mapper.class_
# get the attribute name for the remote column. usually this
# is column.key, but this is a more "complete" check in case
# columns have been custom mapped.
attr_name = prop.mapper._get_col_to_prop(result).key
break
else:
target_class = attr_name = None
if target_class:
sess.query(target_class).filter_by(**{attr_name:d.project_id})
This is what comes to mind just without thinking too deeply. If I can think
of a simpler way to do it, I'll let you know. You're basically looking for a
specific ORM feature without actually using the ORM's normal API, which is why
this isn't covered.
>
> Since I need to issue:
>
> p = sess.query(Project).get(p.id)
>
> is there a way to get Project (the class) from d and 'project_id'
>
> I hope now it's a little bit clearer
>
> sandro
> *:-)
>
>
>
>
> --
> Sandro Dentella *:-)
> http://sqlkit.argolinux.org SQLkit home page - PyGTK/python/sqlalchemy
>
> --
>
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy" group.
> To post to this group, send email to [email protected].
> To unsubscribe from this group, send email to
> [email protected].
> For more options, visit this group at
> http://groups.google.com/group/sqlalchemy?hl=en.
>
>
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
