Hi,
I want to override a relationship in a subclass to relate to a subclass of
the base attributes' related class. Perhaps an example of how I thought it
should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source -> Source and I want
Production_Load.source -> Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a query,
I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
Thanks,
Eric
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