psql sqlalchemy cascade delete

cascade delete

import sqlalchemy
from sqlalchemy import schema
from sqlalchemy import types
from sqlalchemy.orm import relationship
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
 
 
metadata = schema.MetaData()
BaseObject = declarative_base(metadata=metadata)
 
 
class ParentNew(BaseObject):
    __tablename__ = 'parent'
    id = schema.Column(types.Integer(), primary_key=True, autoincrement=True)
    children = relationship('Child', cascade='all,delete-orphan', passive_deletes=True)
 
 
class Child(BaseObject):
    __tablename__ = 'child'
    id = schema.Column(types.Integer(), primary_key=True, autoincrement=True)
    parent_id = schema.Column(types.Integer, schema.ForeignKey('parent.id', ondelete='CASCADE'), nullable=False)
 
engine = sqlalchemy.create_engine('postgresql:///pytest', echo=True)
metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
 
parent = ParentNew()
child = Child()

print '-'*50 + '{0}'.format('after creating')
print parent.children
print '-'*50
session.add(parent)
parent.children.append(child)
session.commit()
print '-'*50 + '{0}'.format('after adding')
print parent.children
print '-'*50
session.flush()
session.delete(child)
session.flush()
print '-'*50 + '{0}'.format('after deleting NO commit')
print parent.children
print '-'*50
session.commit()
print '-'*50 + '{0}'.format('after deleting YES commit')
print parent.children
print '-'*50