Hi again,
I thought I should reply and update on what the issue was.
It might be possible that __declare_last__() isn't appropriate here, can
> you try just saying "Context.link = column_property()"... right after
> you declare Context?
>
This was a good advice and ultimately led me to the solution. Since
__declare_last__ runs for all the subclasses as well I ended up with the
link attribute on both Context and the subclasses. Changing this to limit
it only on Context solved the issue for me.
Thanks!
Mattias L
On Monday, November 2, 2015 at 3:16:07 PM UTC+1, Mattias Lagergren wrote:
>
> Hi,
>
> I'm trying to use load_only and joinedload on a relationship
> model.Asset.parent. The parent relation is polymorphic and can be either
> Task or Project with the common Base class called Context.
>
> import sqlalchemy.orm
> import sqlalchemy.inspection
>
> entity = model.session.query(
> model.Asset
> ).options(
> sqlalchemy.orm.joinedload('parent').load_only(
> 'context_type', 'name', 'link'
> )
> ).first()
>
> state = sqlalchemy.inspection.inspect(entity.parent)
> for attribute in state.attrs:
> is_loaded = (
> attribute.loaded_value is not
> sqlalchemy.orm.base.NO_VALUE
> )
> if is_loaded:
> print attribute.key
>
> # Output:
> id
> taskid
> name
> context_type
>
>
> The id, name and context_type is from Context. And taskid is primary key
> on the taskid and is a foreignkey to the context.id. As you can see
> "name" loads fine but "link" attribute is not loaded. The "link" column is
> added as a column_property to Context using a __declare_last__.
>
> These are simplified versions of the classes:
>
>
> class Context(Base):
> '''Represent a context.'''
> context_type = Column(Unicode(32), nullable=False)
>
> __mapper_args__ = {
> 'polymorphic_on': context_type,
> 'polymorphic_identity': 'context'
> }
>
> name = Column(Unicode(255), default=u'', nullable=False)
>
> @declared_attr
> def id(cls):
> return Column(CHAR(36), primary_key=True, default=lambda: str(uuid
> ()))
>
> @classmethod
> def __declare_last__(cls):
> '''Return link expression query.'''
>
> ...
>
> cls.link = column_property(
> sqlalchemy.type_coerce(
> query, LinkTypeDecorator
> ).label('link')
> )
>
> class Task(Context):
> '''Represent a task.'''
>
> taskid = Column(
> types.CHAR(36),
> ForeignKey('context.id'),
> primary_key=True
> )
>
> __mapper_args__ = {
> 'polymorphic_identity': 'task'
> }
>
>
> class Asset(Base):
> '''Represent an Asset.'''
>
> context_id = sqlalchemy.Column(
> sqlalchemy.CHAR(36), sqlalchemy.ForeignKey('context.id')
> )
>
> parent = relationship('Context', backref=backref('assets'))
>
>
> Can you see if I'm doing something wrong?
>
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