Works great for me
On Tuesday, February 21, 2017 at 2:56:58 PM UTC-6, Shane Carey wrote:
>
> I understand from the docs and several questions both here and on
> bitbucket that cascading polymorphism is not supported. This
> is what it says on the docs:
>
> Warning
>
> Currently, *only one discriminator column may be set*, typically on the
> base-most class in the hierarchy. “Cascading” polymorphic columns are not
> yet supported.
>
>
> However, the following experiment works for me
>
>
> from sqlalchemy import *
>
> from sqlalchemy.orm import *
>
> from sqlalchemy.ext.declarative import declarative_base
>
> import json
>
>
> Base = declarative_base()
>
>
> class Top(Base):
>
> __tablename__ = 'top'
>
>
> id = Column(Integer, primary_key=True)
>
> type = Column(String(8), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_on': type,
>
> 'with_polymorphic': '*'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'id': self.id
>
> }
>
>
> class Primary(Top):
>
> __tablename__ = 'primary'
>
>
> id = Column(None, ForeignKey(Top.id), primary_key=True)
>
> type = Column(String(8), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'primary',
>
> 'polymorphic_on': type,
>
> 'with_polymorphic': '*'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'type': self.type,
>
> **super().dict()
>
> }
>
>
> class One(Primary):
>
> __tablename__ = 'one'
>
>
> id = Column(None, ForeignKey(Primary.id), primary_key=True)
>
> one = Column(String(32), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'one'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'one': self.one,
>
> **super().dict()
>
> }
>
>
> class Two(Primary):
>
> __tablename__ = 'two'
>
>
> id = Column(None, ForeignKey(Primary.id), primary_key=True)
>
> two = Column(String(32), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'two'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'two': self.two,
>
> **super().dict()
>
> }
>
>
> class Secondary(Top):
>
> __tablename__ = 'secondary'
>
>
> id = Column(None, ForeignKey(Top.id), primary_key=True)
>
> type = Column(String(8), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'secondary',
>
> 'polymorphic_on': type,
>
> 'with_polymorphic': '*'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'type': self.type,
>
> **super().dict()
>
> }
>
>
> class Three(Secondary):
>
> __tablename__ = 'three'
>
>
> id = Column(None, ForeignKey(Secondary.id), primary_key=True)
>
> three = Column(String(32), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'three'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'three': self.three,
>
> **super().dict()
>
> }
>
>
> class Four(Secondary):
>
> __tablename__ = 'four'
>
>
> id = Column(None, ForeignKey(Secondary.id), primary_key=True)
>
> four = Column(String(32), nullable=False)
>
>
> __mapper_args__ = {
>
> 'polymorphic_identity': 'four'
>
> }
>
>
> def dict(self):
>
> return {
>
> 'four': self.four,
>
> **super().dict()
>
> }
>
>
> if __name__ == '__main__':
>
> e = create_engine('sqlite:///poly_casc.db', echo=True)
>
>
> Base.metadata.drop_all(e)
>
> Base.metadata.create_all(e)
>
>
> s = create_session(e)
>
>
> s.begin()
>
>
> s.add_all([One(one='one'), Two(two='two'), Three(three='three'),
> Four(four='four')])
>
>
> s.commit()
>
>
> for m in s.query(Top).all():
>
> print(json.dumps(m.dict(), indent=4))
>
> print(type(m))
>
>
> s.expunge_all()
>
>
> for m in s.query(Primary).all():
>
> print(json.dumps(m.dict(), indent=4))
>
> print(type(m))
>
>
> s.expunge_all()
>
>
> for m in s.query(One).all():
>
> print(json.dumps(m.dict(), indent=4))
>
> print(type(m))
>
>
> so I am wondering if the docs needed to be updated, or I am missing
> something regarding the functionality.
>
>
> Thanks
>
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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