Question

我们的生产服务器会终止非活动连接，因此我们的API需要在需要时恢复它们。以下代码有效，但它非常重复：

   private const int MaxRetryCount = 3;

    public static SqlDataReader RestoreConnectionAndExecuteReader(SqlCommand command)
    {
        int retryCount = 0;

        while (retryCount++ < MaxRetryCount)
        {
            try
            {
                if (command.Connection.State == ConnectionState.Closed)
                    command.Connection.Open();
                return command.ExecuteReader();
            }
            catch(Exception e)
            {
                if(!e.Message.ToLower().Contains("transport-level error has occurred"))
                {
                    throw;
                }
            }
        }
        throw new Exception("Failed to restore connection for command:"+command.CommandText);
    }

    public static void RestoreConnectionAndExecuteNonQuery(SqlCommand command)
    {
        var retryCount = 0;
        while(retryCount++ < MaxRetryCount)
        {
            try
            {
                if (command.Connection.State == ConnectionState.Closed)
                    command.Connection.Open();
                command.ExecuteNonQuery();
                return;
            }
            catch(Exception e)
            {
                if (!e.Message.ToLower().Contains("transport-level error has occurred"))
                {
                    throw;
                }
            }
        }
        throw new Exception("Failed to restore connection for command:" + command.CommandText);
    }

我如何重构代码并消除重复？我需要保留这些方法的签名，因为它们在整个系统中使用。

Answer 1

private const int MaxRetryCount = 3;

public static T RestoreConnectionAndExecute<T>(SqlCommand command, Func<SqlCommand, T> func)
{
    int retryCount = 0;

    while (retryCount++ < MaxRetryCount)
    {
        try
        {
            if (command.Connection.State == ConnectionState.Closed)
                command.Connection.Open();
            return func(command);
        }
        catch(Exception e)
        {
            if(!e.Message.ToLower().Contains("transport-level error has occurred"))
            {
                throw;
            }
        }
    }
    throw new Exception("Failed to restore connection for command:"+command.CommandText);

} 

public static SqlDataReader RestoreConnectionAndExecuteReader(SqlCommand command)
{
    return RestoreConnectionAndExecute(command, c => c.ExecuteReader());
}

public static int RestoreConnectionAndExecuteNonQuery(SqlCommand command)
{
    return RestoreConnectionAndExecute(command, c => c.ExecuteNonQuery());
}

Answer 2

private const int MaxRetryCount = 3;

        public static SqlDataReader RestoreConnectionAndExecuteReader(SqlCommand command)
        {
            return RestoreConnectionAndExecuteQueryHelper(command, true);
        }

        public static void RestoreConnectionAndExecuteNonQuery(SqlCommand command)
        {
            RestoreConnectionAndExecuteQueryHelper(command, false);
        }

        private static SqlDataReader RestoreConnectionAndExecuteQueryHelper(SqlCommand command, bool returnReader)
        {
            var retryCount = 0;
            while (retryCount++ < MaxRetryCount)
            {
                try
                {
                    if (command.Connection.State == ConnectionState.Closed)
                        command.Connection.Open();
                    if (returnReader)
                    {
                        return command.ExecuteReader();
                    }
                    else
                    {
                        command.ExecuteNonQuery();
                        return null;
                    }
                }
                catch (Exception e)
                {
                    if (!e.Message.ToLower().Contains("transport-level error has occurred"))
                    {
                        throw;
                    }
                }
            }
            throw new Exception("Failed to restore connection for command:" + command.CommandText);
        }

Answer 3

这些方法的共同部分是连接检索过程。您可以创建一个新的静态方法，该方法负责调用例如以命令作为参数的检索连接，如果在其他情况下建立连接则返回它，则抛出异常。

Answer 4

在代码示例中有一些我不喜欢的东西。但是，要明确回答关于删除重复的问题 - 将公共代码提取到需要委托的方法中。

private TReturn RestoreConnectionAndExecute<T>(SqlCommand command, Func<SqlCommand, TReturn> execute) 
{
   int retryCount = 0;
   while (retryCount++ < MaxRetryCount)
   {
       try
       {
          if (command.Connection.State == ConnectionState.Close) 
              command.Connection.Open();
          return execute(command);
       } 
       catch(Exception e)
       {
          ...
   }
}

public SqlDataReader RestoreConnectionAndExecuteReader(SqlCommand command) 
{
   return this.RestoreConnectionAndExecute(command, c => c.ExecuteReader());
}

public void RestoreConnectionAndExecuteNonQuery(SqlCommand command)
{
   // Ignore return
   this.RestoreConnectionAndExecute(command, c => c.ExecuteNonQuery());
}

但你应该重新考虑一些事情。包括：

捕获特定例外
使用Exception.Number或ErrorCode代替消息（在本地化版本中更改，可能在更新的FX版本中更改）
使用IDisposable资源的语句
抛出特定例外

如何重用重新打开连接的代码？

4 个答案: