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from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
 
Base = declarative_base()
 
class Association(Base):
    __tablename__ = 'exmp_association'
    parent_id = Column(Integer, ForeignKey('exmp_parent.id', ondelete='CASCADE'), primary_key=True)
    child_id = Column(Integer, ForeignKey('exmp_child.id', ondelete='CASCADE'), primary_key=
    extra_data = Column(String(50))
 
class Parent(Base):
    __tablename__ = 'exmp_parent'
    id = Column(Integer, primary_key=True)
    associations = relationship("Association", backref="parent")
  
class Child(Base):
    __tablename__ = 'exmp_child'
    id = Column(Integer, primary_key=True)
    associations = relationship("Association", backref="child")

s = get_session()
p = Parent()
a = Association()
c = Child()
a.child = c
p.associations.append(a)
s.add(p)
s.commit()
a = s.query(Association).get([1, 1])
print(s.query(Parent).count())
print(s.query(Association).count())
print(a.parent)
print(a.child)
s.query(Parent).delete()
s.commit()
print(s.query(Parent).count())
print(s.query(Association).count())

class Association(Base):
    __tablename__ = 'exmp_association'
    parent_id = Column(Integer, ForeignKey('exmp_parent.id'), primary_key=True)
    child_id = Column(Integer, ForeignKey('exmp_child.id'), primary_key=True)
    extra_data = Column(String(50))
 
class Parent(Base):
    __tablename__ = 'exmp_parent'
    id = Column(Integer, primary_key=True)
    associations = relationship("Association", backref="parent", cascade='all, delete-orphan')
 
class Child(Base):
    __tablename__ = 'exmp_child'
    id = Column(Integer, primary_key=True)
     associations = relationship("Association", backref="child", cascade='all, delete-orphan')

sqlalchemy.exc.IntegrityError: (IntegrityError) update or delete on table "exmp_parent" violates foreign key constraint "exmp_association_parent_id_fkey" on table "exmp_association"
DETAIL:  Key (id)=(1) is still referenced from table "exmp_association".
 'DELETE FROM exmp_parent' {}