Hello.
Is there any way I can use some expression for polymorphic_on mapper
attribute?
I have tried some ways, but not got what I want.
# --- my tries
import sqlalchemy as sa
from sqlalchemy import *
from sqlalchemy import orm
from sqlalchemy.ext.declarative import declarative_base
_decl = declarative_base()
class generic(_decl):
__tablename__ = 'generic'
idnr = Column(Integer, primary_key=True)
type = Column(String(32), nullable=False)
data = Column(String(128))
discriminator = orm.column_property(case(value=type, whens={'abc':type,
'cde':type}, else_='generic').label('discriminator'))
__mapper_args__ = {'polymorphic_on': type,
'polymorphic_identity':'generic'}
#__mapper_args__ = {'polymorphic_on': discriminator,
'polymorphic_identity':'generic'}
#__mapper_args__ = {'polymorphic_on': case(value=type,
whens={'abc':type, 'cde':type}, else_='generic'),
'polymorphic_identity':'generic'}
class type_abc(generic):
__tablename__ = 'abc'
generic_idnr = Column(Integer, ForeignKey(generic.idnr,
onupdate='CASCADE', ondelete='CASCADE'), primary_key=True)
abc = Column(Integer, nullable=False)
__mapper_args__ = {'polymorphic_identity':'abc'}
class type_cde(generic):
__tablename__ = 'cde'
generic_idnr = Column(Integer, ForeignKey(generic.idnr,
onupdate='CASCADE', ondelete='CASCADE'), primary_key=True)
cde = Column(Integer, nullable=False)
__mapper_args__ = {'polymorphic_identity':'cde'}
def main():
engine = create_engine('sqlite:///:memory:', echo=True)
generic.metadata.create_all(engine)
sm = orm.sessionmaker(bind=engine)
ses = sm()
a = type_cde()
a.cde = 1
ses.add(a)
a = type_abc()
a.abc = 2
ses.add(a)
#pdb.set_trace()
a = generic()
a.type = 'zzz'
a.data = 'a vot tak?'
ses.add(a)
ses.commit()
if __name__ == '__main__':
main()
# ---- code end
It works only with real column instance...
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