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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