如何显示数据集的数量C＃ [英] How to show numbers of datasets C#

问题描述

您好我想在点击按钮后显示数据集的数量。但是，如果我单击按钮程序崩溃。错误消息是： ConnectionString属性未初始化



我的代码：

 private void button2_Click_1（object sender，EventArgs e）
 {
 this.timer1.Start（）; 
 
 SqlCeConnection conn; 
 SqlCeCommand cmd; 
 SqlCeDataReader rdr; 
 
 conn = new SqlCeConnection（）; 
 cmd = new SqlCeCommand（SELECT COUNT（*）FROM Pigeons，conn）; 
 conn.Open（）; 
 MessageBox.Show（cmd.ExecuteScalar（）。ToString（））; 

我尝试过：



我在互联网上查找但我找不到任何解决方案。

解决方案

< blockquote>嗯，是的 - 它会。看代码：

 conn = new SqlCeConnection（）; 
 cmd = new SqlCeCommand（SELECT COUNT（*）FROM Pigeons，conn）; 
 conn.Open（）; 
 

您已经创建了一个连接对象，但是您没有告诉它您希望它连接到什么！ SqlCE是一个基于文件的数据库：您必须至少指定要使用的文件，并将该信息提供给您的SqlCEConnection实例。

SQL Server Compact连接字符串 - ConnectionStrings.com [ ^ ]

 string strConnect = @Data Source = MyFolder\MyData.sdf; Persist Security Info = False ;; 
 conn = new SqlCeConnection（strConnect）; 
 cmd = new SqlCeCommand（SELECT COUNT（*）FROM Pigeons，conn）; 
 conn.Open（）; 
 

Hello I want to show the number of datasets after klicking a button. But if i click the Button the Program crashes. The error message is: The ConnectionString property was not initialized

My code:

private void button2_Click_1(object sender, EventArgs e)
        {
            this.timer1.Start();

            SqlCeConnection conn;
            SqlCeCommand cmd;
            SqlCeDataReader rdr;
                
                conn = new SqlCeConnection();
                cmd = new SqlCeCommand("SELECT COUNT(*) FROM Pigeons", conn);
                conn.Open();
                MessageBox.Show(cmd.ExecuteScalar().ToString());

What I have tried:

I looked up in the internet but I couldn't find any solution.

解决方案

Well, yes - it will. Look at the code:

conn = new SqlCeConnection();
cmd = new SqlCeCommand("SELECT COUNT(*) FROM Pigeons", conn);
conn.Open();

You have created a connection object, but you don't tell it what you want it to connect to! SqlCE is a file-based database: you have to at the very minimum specify the file you want to use and provide that info to your SqlCEConnection instance.
SQL Server Compact connection strings - ConnectionStrings.com[^]

string strConnect = @"Data Source=MyFolder\MyData.sdf;Persist Security Info=False;";
conn = new SqlCeConnection(strConnect);
cmd = new SqlCeCommand("SELECT COUNT(*) FROM Pigeons", conn);
conn.Open();

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