SQLAlchemy 删除

from sqlalchemy import Integer, Column, String, ForeignKey, DateTime, func
from sqlalchemy.orm import declarative_base, relationship, backref, sessionmaker
from sqlalchemy import create_engine

Base = declarative_base()


class Department(Base):
    __tablename__ = 'department'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    city = Column(String)


class Employee(Base):
    __tablename__ = 'employee'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    hired_on = Column(DateTime, default=func.now())
    department_id = Column(Integer, ForeignKey('department.id'))
    department = relationship(Department, backref=backref('employees', uselist=True, cascade='delete,all'))
    age = Column(Integer)


engine = create_engine("sqlite:///")
session = sessionmaker()
session.configure(bind=engine)
Base.metadata.create_all(engine)

s = session()
it_department = Department(name='IT')


financial_department = Department(name='Finance')
financial_department.city = 'Beijing'
s.add(financial_department)
print(s.query(Department).count())

for department in s.query(Department).all():
    print(department.name, department.city)
    s.delete(department)

print(s.query(Department).count())