Update functions/sql example to use more clear connection logic. (#2486)

Author: kurtisvg

functions/sql/mysql_sample.py

@@ -16,14 +16,16 @@
 from os import getenv
 
 import pymysql
-from pymysql.err import OperationalError
 
 # TODO(developer): specify SQL connection details
 CONNECTION_NAME = getenv('MYSQL_INSTANCE', '<YOUR INSTANCE CONNECTION NAME>')
 DB_USER = getenv('MYSQL_USER', '<YOUR DB USER>')
 DB_PASSWORD = getenv('MYSQL_PASSWORD', '<YOUR DB PASSWORD>')
 DB_NAME = getenv('MYSQL_DATABASE', '<YOUR DB NAME>')
 
+# set to true to test locally using Cloud SQL proxy listening on a TCP port
+DEBUG = False
+
 mysql_config = {
   'user': DB_USER,
   'password': DB_PASSWORD,
@@ -56,12 +58,14 @@ def mysql_demo(request):
     # GCF instance. Doing so minimizes the number of active SQL connections,
     # which helps keep your GCF instances under SQL connection limits.
     if not mysql_conn:
-        try:
-            mysql_conn = pymysql.connect(**mysql_config)
-        except OperationalError:
-            # If production settings fail, use local development ones
-            mysql_config['unix_socket'] = f'/cloudsql/{CONNECTION_NAME}'
-            mysql_conn = pymysql.connect(**mysql_config)
+        if DEBUG:
+            # try to connect using localling running Cloud SQL proxy
+            # (local development only)
+            mysql_conn = pymysql.connect(
+              **mysql_config, host='127.0.0.1', port=3306)
+        else:
+            mysql_conn = pymysql.connect(
+              **mysql_config, unix_socket=f'/cloudsql/{CONNECTION_NAME}')
 
     # Remember to close SQL resources declared while running this function.
     # Keep any declared in global scope (e.g. mysql_conn) for later reuse.