C＃抛出异常会引发另一个异常 [英] C# throwing exceptions throws another exception

问题描述

我有一个异常抛出问题，我的程序通过OleDB连接与访问数据库一起工作。

这是我的函数导致错误。

Im having a exception throwing problem with my program which works with a access database through OleDB connection.
Here is my function which causes the error.

public static string getNICByID(int ID)
        {
            //validation params
            if (ID <= 0)
                throw new Exception("Invalid ID");
            //if (!isRegNumExists(ID))
            //    throw new Exception("No records");


            const string query = @"select NICNumber from Student where StudentRegNo = @_regNum";

            try
            {
                using (OleDbConnection con = new OleDbConnection(conString))
                {
                    con.Open();

                    using (OleDbCommand cmd = new OleDbCommand(query, con))
                    {
                        cmd.Parameters.Add("@_regNum", OleDbType.Integer).Value = ID;

                        object obj = cmd.ExecuteScalar();
                        if (obj != null)
                            return obj.ToString();
                        else
                            throw new Exception("No records");
                    }
                }
            }
            catch { throw; }

如果数据表包含有关ID的记录，则此函数可以正常工作并返回我想要的内容。但如果表中没有包含记录，则会抛出另一个异常，如下图所示。



http://s7.postimg.org/w4j72ie8b/Untitled.png [ ^ ]



我的代码有什么问题？



提前谢谢。

This functions works fine and returns what I want if the data table contains a record with respect to the ID. But if the table doesnt contain a record it throws another exception like the picture below.

http://s7.postimg.org/w4j72ie8b/Untitled.png[^]

What's the wrong with my code ?

Thanks in advance.

推荐答案

这是因为当你在数据库中找不到记录时，你本人就会在你的代码中抛出这个异常。

That is because you, yourself, personally are throwing this exception in your code when there is no record found in the database.

if (obj != null)
     return obj.ToString();
else
     throw new Exception("No records");

这行代码旨在满足您的需求。它会看到，如果有任何记录，则以其他方式抛出异常;以参数为原因或消息。



要忽略引发的异常，请删除此行，

This line of code is intended to do what you're seeing. It will see, if there is any record, ortherwise throw the exception; with the parameter as the reason or Message.

To ignore the exception being raised, please remove this line,

throw new Exception("No records");

然后它不会抛出异常，而是你可以用这个值显示一条消息弹出给用户。

Then it won't throw the exception, instead you can show a message pop up to the user with this value.

你'再次在你的catch（）部分再次抛出Excetion。

You're throwing the Excetion again in your catch() section.

try
{
    // your code
    throw New Exception ("no recors")
}
catch (throw)  
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}

其他两个答案显示了正在发生的事情。我会做的是



将你的试试块更改为

The other two answers are showing you what is going on. What I would do is

change your try catch block to

try
{
   if (obj != null)
       return obj.ToString();
   else
       throw new Exception("No records");
}
catch(Exception ex)
{
  //put a break point on this line below
  String message = ex.message;
}

我会在字符串消息行上设置断点，然后在调试时检查ex。消息，因为它会告诉你错误信息应该是没有记录



我个人也会将你的异常更改为更合适的东西，比如SQLExcpetion而不是catch所有异常

I would put a breakpoint on the string message line and then while debugging check the ex.message as it will show you that the error message should be "No Records"

I personally would also change your exception to something more appropriate such as SQLExcpetion rather than the catch all Exception

这篇关于C＃抛出异常会引发另一个异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！