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/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
---
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at https://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
