sqlalchemy create_engine（）（如果数据库已经存在）

Question

from pox.core import core
import pox.openflow.libopenflow_01 as of
import re
import datetime

from sqlalchemy import create_engine, ForeignKey
from sqlalchemy import Column, Date, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, backref
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker


log = core.getLogger()



engine = create_engine('sqlite:///nwtopology.db', echo=False)
Base = declarative_base()
Session = sessionmaker(bind=engine)
session = Session()

if I create call the last four python statements repeateadly by restarting the program will it have a negative impact on the correct functioning of the database.? Will it create the database again if one already exists?

Answer 1

As sberry wrote - calling create_engine and creating session multiple times by rerunning same script will just open connection and create SQLAlchemy engine object with reference to this connection. Thus doing so won't create new sqlite database file and won't impact the database functioning.

Also I would suggest to make sure that your code always do session.close() at the end of your script. This would ensure that all changes if there were any will be committed to database. By changes I mean any updates/inserts your script may do to database.