如何在C＃应用程序中定义和使用连接字符串 [英] How do I define and use a connection string in my C# app

问题描述

您好我想知道如何定义连接字符串并在我的应用程序中成功使用它。想法是定义一次并根据需要使用。

我按照这里的建议：



如何从C＃中的App.Config获取连接字符串 [ ^ ]



收效甚微。当我运行我的测试应用程序时，它运行正常，但当我要求它将唯一值插入我为该场合创建的测试数据库时，我有一条错误消息：



对象引用未定义到对象的实例在语句的级别

Hi I wish to know how to define a connection string and use it successfully in my App. The Idea is to define once and use as required.
I followed the advice here :

How to get Connection String from App.Config in C#[^]

with little success. when i run my test app, it runs ok but when i ask it to insert sole values into the test database I created for the occasion i have an error message:

" Object reference is not defined to an instance of the object " at the level of the statement

var connectionString = ConfigurationManager.ConnectionStrings["con"].ConnectionString;

我应该做些什么来解决这个问题呢？



我尝试过：



1.首先我在config.app文件中添加了这段代码：

What should I do to get this situation sorted out please ?

What I have tried:

1. First I added this code in the config.app file:

<connectionStrings>
    <add name= "con" 
         providerName= "System.Data.SqlClient" 
         connectionString="Data Source=.\sqlexpress;Initial Catalog=practice;Integrated Security=True" />
    </connectionStrings>

2.接下来我添加了对System.Configuration的引用



3.我的按钮控件的click事件包含以下代码：

2. Next I Added a reference to System.Configuration

3. The click event of my button control has the code :

var connectionString = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
            
            string ins = @"insert into employee(name, address, phonenum, profession) values(@nam, @add, @phonen, @job)";

                SqlCommand cmd = new SqlCommand(ins, con);
                SqlParameter NM = new SqlParameter();
                NM.ParameterName = "nam";
                NM.Value = nametxt.Text;

                SqlParameter AD = new SqlParameter();
                AD.ParameterName = "add";
                AD.Value = addresstxt.Text;

                SqlParameter PN = new SqlParameter();
                PN.ParameterName= "phonen";
                PN.Value = telephonetxt.Text;

                SqlParameter PF = new SqlParameter();
                PF.ParameterName = "job";
                PF.Value = professiontxt.Text;

                cmd.Parameters.Add(AD);
                cmd.Parameters.Add(PN);
                cmd.Parameters.Add(NM);
                cmd.Parameters.Add(PF);
                con.Open();
                cmd.ExecuteNonQuery();
                MessageBox.Show("Values Entered", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                con.Close();

推荐答案

嘿伙计们，我找到了缺少的小东西：

这实际上是这样的：

Hey Guys, I found the little thing that was lacking:
This actually did it:

private void btn_enter_Click(object sender, EventArgs e)
{
var connectionString = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
 
SqlConnection cn= new SqlConnection(connectionString); //This is all I had to add
string ins = @"insert into employee(name) values(@nam)";

SqlCommand cmd = new SqlCommand(ins, cn);//Brought in a few modifications 
SqlParameter NM = new SqlParameter();
NM.ParameterName = "nam";
NM.Value = txtboxname.Text;
cmd.Parameters.Add(NM);
cn.Open();
cmd.ExecuteNonQuery();
MessageBox.Show("Values Entered", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
cn.Close();

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