python - 数据库重启时 SqlAlchemy 崩溃

Question

我的代码如下所示：

from sqlalchemy import create_engine, Column, String, Integer
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import as_declarative


db_url = f'mysql://{user}:{password}@{host}:{port}/{database}'
engine = create_engine(db_url)
db = scoped_session(sessionmaker(bind=engine))


@as_declarative()
class Base(object):
    id = Column(Integer, primary_key=True)
    query = db.query_property()


class User(Base):
    email = Column(String(128), unique=True, nullable=False)

    def __repr__(self):
        return f'<User {self.email}>'

一切正常，直到数据库重新启动。然后db.rollback()是需要的。

例子：

>>> User.query.all()                 
[<User [e-mail]>, <User [e-mail]>]                              
>>> # DB restarted   
...                                                                                            
>>> User.query.all()                           
Traceback (most recent call last):                                                                           
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1244, in _execute_context
    cursor, statement, parameters, context                                                     
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/default.py", line 552, in do_execute
    cursor.execute(statement, parameters)                                                                      
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 206, in execute
    res = self._query(query)                                                                                   
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 312, in _query
    db.query(q)                                                                                          
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/connections.py", line 224, in query
    _mysql.connection.query(self, query)                                                                        
MySQLdb._exceptions.OperationalError: (2006, 'MySQL server has gone away')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>                                                                    
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3161, in all
    return list(self)                                                                                         
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3317, in __iter__
    return self._execute_and_instances(context)                                                                                                                                                                                       
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3342, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 988, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 287, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1107, in _execute_clauseelement
    distilled_params,
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1248, in _execute_context
    e, statement, parameters, cursor, context
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1466, in _handle_dbapi_exception
    util.raise_from_cause(sqlalchemy_exception, exc_info)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 383, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 128, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1244, in _execute_context
    cursor, statement, parameters, context
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/default.py", line 552, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 206, in execute
    res = self._query(query)
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 312, in _query
    db.query(q)
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/connections.py", line 224, in query
    _mysql.connection.query(self, query)
sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError) (2006, 'MySQL server has gone away')
[SQL: SELECT user.id AS user_id, user.email AS user_email, user.token_id AS user_token_id
FROM user]
(Background on this error at: http://sqlalche.me/e/e3q8)
>>> User.query.all()
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1177, in _execute_context
    conn = self._revalidate_connection()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 463, in _revalidate_connection
    "Can't reconnect until invalid "
sqlalchemy.exc.InvalidRequestError: Can't reconnect until invalid transaction is rolled back

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3161, in all
    return list(self)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3317, in __iter__
    return self._execute_and_instances(context)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3342, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 988, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 287, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1107, in _execute_clauseelement
    distilled_params,
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context
    e, util.text_type(statement), parameters, None, None
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1466, in _handle_dbapi_exception
    util.raise_from_cause(sqlalchemy_exception, exc_info)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 383, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 128, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 1177, in _execute_context
    conn = self._revalidate_connection()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/engine/base.py", line 463, in _revalidate_connection
    "Can't reconnect until invalid "
sqlalchemy.exc.StatementError: (sqlalchemy.exc.InvalidRequestError) Can't reconnect until invalid transaction is rolled back
[SQL: SELECT user.id AS user_id, user.email AS user_email, user.token_id AS user_token_id
FROM user]
[parameters: [{}]]
>>> db.rollback()
>>> User.query.all()
[<User [e-mail]>, <User [e-mail]>]

即使在重新连接数据库后，我也希望一切正常。你知道怎么做吗？

标签： pythonmysqlpython-3.xsqlalchemy