Implementing add, delete, modify and query operations on MySQL based on sqlalchemy

from sqlalchemy import exists, Column, Integer, String, ForeignKey, exists
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

# Created database engine engine = create_engine("mysql+pymysql://user:pwd@ip/database name?charset=utf8")

#Create session type DBSession = sessionmaker(bind=engine)

# Instantiate the official model - Base is the ORM model Base = declarative_base()


# Create a service order table class ServiceOrder(Base):
  __tablename__ = 'serviceOrderTable'
  id = Column(Integer, primary_key=True, autoincrement=True)
  serviceOrderId = Column(String(32), nullable=False, index=True, comment='Service Order ID')
  serviceDesc = Column(String(268), comment='Service Description')
  oneLevelName = Column(String(32), comment='C Category')
  twoLevelName = Column(String(32), comment='T subclass')
  threeLevelName = Column(String(32), comment='I project')
  fourLevelName = Column(String(32), comment='S sub-item')
  transferTimes = Column(String(32), comment='Number of transfers')
  overDueStatus = Column(String(32), comment='Expired status')
  serviceTimeLimit = Column(String(32), comment='Service time limit')
  serTimeLimitTypeName = Column(String(16), comment='Time limit type')  
  # One-to-many:
  # serviceWorkOrder = relationship("ServiceWorkOrder", backref="serviceorder")


# Many-to-one: Multiple service orders can belong to the service order class ServiceWorkOrder(Base):
  __tablename__ = 'serviceWorkOrderTable'
  id = Column(Integer, primary_key=True, autoincrement=True)
  serviceWorkOrderId = Column(String(32), nullable=False, index=True, comment='Service Work Order ID')
  workOrderName = Column(String(268), comment='Work Order Name')
  fromId = Column(String(32), comment='Service Order ID')
  createUserSectionName = Column(String(32), comment='Create User Section')
  createUserName = Column(String(32), comment='creator')
  handlerName = Column(String(32), comment='Handler')
  statusName = Column(String(32), comment='Work order status')
  createTime = Column(String(32), comment='Creation time') 
  # The book table on the "many" side is linked to the user table via a foreign key:
  # serviceOrder_id = Column(Integer, ForeignKey('serviceOrderTable.id'))

# Create a database. If the database already exists, it will not be created. It will directly connect to the existing library according to the library name. def init_db():
  Base.metadata.create_all(engine)

def drop_db():
  Base.metadata.drop_all(engine)

def insert_update():
  # all_needed_data_lists is the data format that needs to be inserted into the database [{key: value, ... }, { }, { }...]
  for item in all_needed_data_lists:
    ServiceOrderRow = ServiceOrder(serviceOrderId=item['serviceOrderId'],
                    serviceDesc=item['serviceDesc'],
                    oneLevelName=item['oneLevelName'],
                    twoLevelName=item['twoLevelName'],
                    threeLevelName=item['threeLevelName'],
                    fourLevelName=item['fourLevelName'],
                    transferTimes=item['transferTimes'],
                    overDueStatus=item['overDueStatus'],
                    serviceTimeLimit=item['serviceTimeLimit'],
                    serTimeLimitTypeName=item['serTimeLimitTypeName'],
                    )
    try:
      # Use exists to determine whether the target object exists and return True or Faults
      it_exists = session.query(
          exists().where(ServiceOrder.serviceOrderId == item['serviceOrderId'] )
        ).scalar()
    except Exception as e:
      self.log.error(e)
      break
    try:
      # If it does not exist, add it; if it does exist, update the existing data if not it_exists:
        session.add(ServiceOrderRow)
      else:
        session.query(ServiceOrder).filter(ServiceOrder.serviceOrderId == item['serviceOrderId'])\
          .update(item)
    except Exception as e:
      self.log.error(e)
      break
  try:
    session.commit()
    self.log.info('Data updated successfully!')
  except:
    session.rollback()
    self.log.info('Data update failed!')

if __name__ == "__main__":
  # Create a database. If the database already exists, it will not be created. It will directly connect to the existing library according to the library name. init_db()
  # Create a session object to add, delete, modify and query:
  session = DBSession()
  # Use session to add or modify data. Remember to submit insert_update()