fix

AutoTurnOver.DB/Base/connectionHelper.cs

@@ -47,9 +47,10 @@ namespace AutoTurnOver.DB
         void IDisposable.Dispose()
         {
             _connection.Dispose();
+            __connection = null;
         }
 
-        public static MySqlConnection __connection;
+        private static MySqlConnection __connection;
         public static MySqlConnection _connection
         {
             get
@@ -61,7 +62,7 @@ namespace AutoTurnOver.DB
                 return __connection;
             }
         }
-        public static MySqlConnection __connection_read_only;
+        private static MySqlConnection __connection_read_only;
         public static MySqlConnection _connection_read_only
         {
             get
@@ -82,7 +83,7 @@ namespace AutoTurnOver.DB
         public void Close()
         {
             _connection.Close();
-
+            __connection = null;
         }
         public int Execute(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null)
         {