Question

我有一个简单的crud应用程序，我想按照他们的说法优雅地处理错误。

我只是没有尝试抓住。在我去C＃学校之前，我开始学习一些python，但它并没有真正起作用。这是我的代码，

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Text;
using System.Threading.Tasks;

namespace Crud
{
    class Program
    {
        static string conn_string = "Data Source=MY_SQLSERVER;Initial Catalog=A_DATABASE";

        private static void Create(string name, string email)
        {
            using (SqlConnection conn = new SqlConnection(conn_string))
            {
                SqlCommand cmd = conn.CreateCommand();

                cmd.CommandText = @"INSERT INTO dbo.Person (name, email)
                                    VALUES (@name, @email)";
                cmd.Parameters.AddWithValue("@name", name);
                cmd.Parameters.AddWithValue("@email", email);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
            }
        }

        private static void Read()
        {
            using (SqlConnection conn = new SqlConnection(conn_string))
            {
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = @"SELECT id, name, email FROM dbo.Person ORDER BY id";
                conn.Open();

                using (SqlDataReader dr = cmd.ExecuteReader())
                {
                    while (dr.Read())
                        Console.WriteLine("{0}\t{1}\t{2}", dr.GetInt32(0), dr.GetString(1), dr.GetString(2));
                }
                conn.Close();
            }
        }


        private static void Update(int id, string name, string email)
        {
            using (SqlConnection conn = new SqlConnection(conn_string))
            {
                SqlCommand cmd = conn.CreateCommand();

                cmd.CommandText = @"UPDATE dbo.Person SET name=@name, email=@email
                                    WHERE id = @id";
                cmd.Parameters.AddWithValue("@id", id);
                cmd.Parameters.AddWithValue("@name", name);
                cmd.Parameters.AddWithValue("@email", email);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
            }
        }

        private static void Delete(int id)
        {
            using (SqlConnection conn = new SqlConnection(conn_string))
            {
                SqlCommand cmd = conn.CreateCommand();

                cmd.CommandText = @"DELETE FROM dbo.Person WHERE id=@id";
                cmd.Parameters.AddWithValue("@id", id);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
            }
        }

        static void Main(string[] args)
        {
            Console.WriteLine("Please Enter a Command (Create, Read, Update or Delete)");
            string input = Console.ReadLine();

            if (input == "Read" || input == "read")
            {
                Read();
                Console.WriteLine("");
            }
            else if (input == "Create" || input == "create")
            {
                Console.WriteLine("Enter a name");
                string name = Console.ReadLine();
                Console.WriteLine("Enter an email address");
                string email = Console.ReadLine();

                Create(name, email);
                // Assuming Create has not yet returned an error, everything successful
                Console.WriteLine("Entry Created Successfully!");
            }
            else if (input == "Update" || input == "update")
            {
                int id;
                bool check;
                do
                {
                    Console.WriteLine("What id would you like to change?");
                    string val = Console.ReadLine(); 
                    check = int.TryParse(val, out id);
                } while (!check);
                Console.WriteLine("Enter a name");
                string name = Console.ReadLine();
                Console.WriteLine("Enter an email address");
                string email = Console.ReadLine();

                Update(id, name, email);
                Console.WriteLine("Entry Updated Successfully!");
            }
            else if (input == "Delete" || input == "delete")
            {
                int id;
                bool check;
                do
                {
                    Console.WriteLine("What id would you like to delete?");
                    string val = Console.ReadLine(); 
                    check = int.TryParse(val, out id);
                } while (!check);

                Delete(id);
                Console.WriteLine("Entry Deleted Successfully :(");
            }
        }
    }
}

它有效，但它很脆弱。这是一个控制台应用程序，我有一天会变成一个HTML解决方案，但是......

我不确定将try catch块放在哪里，我不知道在哪里放置异常。然后我在msdn上，他们告诉我他们终于使用了。最后，我能理解的东西。所以，来自python我会说尝试显然是一样的，c sharp中的catch (){}就像python中的except:但是我没有在python中使用参数。我是个小伙子。我想我可以在.NET中使用Exception对象，但我不需要它。如果发生任何错误，我只想写一个自定义消息...我的意思是，写一个href有多难？我无法让它正常工作。

所以我的问题是，如果我想在每个crud操作中保留try catch块，我将如何构造Create方法？

Answer 1

基本C＃异常处理：

try
{
    //do stuff
}
catch 
{
    //write custom exception message
}
finally
{
    //this is not necessary, but would be here
}

catch块将捕获上例中的所有异常。如果你想对异常做一些事情，你可以这样做：

catch (Exception e)
{
    //do something with e
}

在您的情况下，它看起来像：

private static void Create(string name, string email)
    {
        try
        {
            using (SqlConnection conn = new SqlConnection(conn_string))
            {
                SqlCommand cmd = conn.CreateCommand();

                cmd.CommandText = @"INSERT INTO dbo.Person (name, email)
                                    VALUES (@name, @email)";
                cmd.Parameters.AddWithValue("@name", name);
                cmd.Parameters.AddWithValue("@email", email);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
            }
        }
        catch
        {
            //print custom error message
        }
    }

错误和异常处理

1 个答案: