發現問題
最近使用 Flask+MySQL 寫了些簡單的接口，部署到Linux之后，發現過了一段時間，再次訪問接口就不能用了，報錯如下：
Traceback (most recent call last):
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 2328, in __call__
return self.wsgi_app(environ, start_response)
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 2314, in wsgi_app
response = self.handle_exception(e)
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 1760, in handle_exception
reraise(exc_type, exc_value, tb)
File "/root/python36/lib/python3.6/site-packages/flask/_compat.py", line 36, in reraise
raise value
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 2311, in wsgi_app
response = self.full_dispatch_request()
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 1834, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 1737, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/root/python36/lib/python3.6/site-packages/flask/_compat.py", line 36, in reraise
raise value
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 1832, in full_dispatch_request
rv = self.dispatch_request()
File "/root/python36/lib/python3.6/site-packages/flask/app.py", line 1818, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/root/flaskDemo/api/user.py", line 18, in get_all_users
data = db.select_db(sql)
File "/root/flaskDemo/common/mysql_operate.py", line 27, in select_db
self.cur.execute(sql)
File "/root/python36/lib/python3.6/site-packages/pymysql/cursors.py", line 170, in execute
result = self._query(query)
File "/root/python36/lib/python3.6/site-packages/pymysql/cursors.py", line 328, in _query
conn.query(q)
File "/root/python36/lib/python3.6/site-packages/pymysql/connections.py", line 516, in query
self._execute_command(COMMAND.COM_QUERY, sql)
File "/root/python36/lib/python3.6/site-packages/pymysql/connections.py", line 750, in _execute_command
raise err.InterfaceError("(0, '')")
pymysql.err.InterfaceError: (0, '')
在網上查了下，是因為這個數據庫的連接建立太久了，會自動斷開，這個時候我們需要重新建立連接，否則訪問接口就會出現異常報錯了。
解決辦法
在知道了問題原因后，我們就需要進行處理了。上面說到MySQL連接時間太長了會斷開連接，那么我們可以在每次操作SQL之前對連接進行檢查，如果發現連接已經斷開，則進行重連。
在 pymysql 創建的數據庫連接對象下，有這么一個方法：
ping()，直接進去查看源碼。
def ping(self, reconnect=True):
"""
Check if the server is alive.
:param reconnect: If the connection is closed, reconnect.
:raise Error: If the connection is closed and reconnect=False.
"""
if self._sock is None:
if reconnect:
self.connect()
reconnect = False
else:
raise err.Error("Already closed")
try:
self._execute_command(COMMAND.COM_PING, "")
self._read_ok_packet()
except Exception:
if reconnect:
self.connect()
self.ping(False)
else:
raise
在源碼中，如果使用了該方法 ping(reconnect=True) ，那么可以在每次連接之前，會檢查當前連接是否已關閉，如果連接關閉則會重新進行連接，於是我們可以將其用於處理目前報錯的問題，改動后的代碼如下：
def select_db(self, sql):
"""查詢"""
# 檢查連接是否斷開，如果斷開就進行重連
self.conn.ping(reconnect=True)
# 使用 execute() 執行sql
self.cur.execute(sql)
# 使用 fetchall() 獲取查詢結果
data = self.cur.fetchall()
return data
def execute_db(self, sql):
"""更新/新增/刪除"""
try:
# 檢查連接是否斷開，如果斷開就進行重連
self.conn.ping(reconnect=True)
# 使用 execute() 執行sql
self.cur.execute(sql)
# 提交事務
self.conn.commit()
except Exception as e:
print("操作出現錯誤：{}".format(e))
# 回滾所有更改
self.conn.rollback()
上面的處理，其實只是在 select_db() 和 execute_db() 中使用 execute() 方法執行sql前，加了一行代碼：self.conn.ping(reconnect=True) ，而 self.conn 則是代碼里創建的 pymysql 數據庫連接對象，我按上述方法處理之后問題得以解決。