I'm using aiohttp
and sqlalchemy
, and I've created a Singleton that helps me to connect when I'm needed a instance of SQLAlchemy (code follows).
Unfortunately, every once in awhile I get the following error (which I "solve" by restarting the server):
Dec 11 09:35:29 ip-xxx-xxx-xxx-xxx gunicorn[16513]: sqlalchemy.exc.StatementError: (sqlalchemy.exc.InvalidRequestError) Can't reconnect until invalid transaction is rolled back [SQL: '... \nFROM ...\nWHERE ... = %(username_1)s \n LIMIT %(param_1)s'] [parameters: [{}]]```
Is there any way to fix the current code? Thanks :)
CONNECTION_DETAILS = {
'driver': 'pymysql',
'dialect': 'mysql',
'host': os.environ.get('HOST'),
'port': 3306,
'user': 'master',
'password': os.environ.get('PASSWORD'),
'database': 'ourdb',
'charset': 'utf8'
}
_instance = None
def __new__(cls, *args, **kwargs):
if not cls._instance:
con_str = '{dialect}+{driver}://{user}:{password}@' \
'{host}:{port}/{database}?charset={charset}'\
.format(**cls.CONNECTION_DETAILS)
try:
engine = sqlalchemy.create_engine(con_str)
Session = scoped_session(sessionmaker(bind=engine))
session = Session() # Create the ORM handle
except sqlalchemy.exc.OperationalError:
logger.exception('Establishing database connection error.')
cls._instance = super().__new__(cls)
logger.debug("Returning database's session.")
cls._instance.session = session
# Initializing tables
cls._instance.Users = Users
cls._instance.Services = Services
cls._instance.APIKeys = APIKeys
return cls._instance
This would be a fairly late answer. This is what happens: While using the session, a sqlalchemy Error is raised (anything which would also throw an error when be used as pure SQL: syntax errors, unique constraints, key collisions etc.).
You would have to find this error, wrap it into a try/except
-block and perform a session.rollback()
.
After this you can reinstate your session.