如何在C＃程序中包含此代码

Question

I am running into problems with my Database not opening because it is already, apparently, open.

Unable to copy file "j:...\\KAELC_DB.mdf" to "bin\\Debug\\KAELC_DB.mdf". The process cannot access the file 'j:...\\KAELC_DB.mdf' because it is being used by another process.

Unable to copy file "j:...\\KAELC_DB_log.ldf" to "bin\\Debug\\KAELC_DB_log.ldf". The process cannot access the file 'j:...\\KAELC_DB_log.ldf' because it is being used by another process.

I found a reply to an old question on StackExchange, linked to here https://stackoverflow.com/a/3998383 , by "Justin", which looks to resolve that problem (and I have also read in other places that "using" is one of the most efficient ways of programming in C#) but how do I use this in my code ?

I have created a small Project that does nothing but allow me to press a button in order to process a SQL statement, but I'm confused as to what "Justin" means by "Use the connection" ... how do I put SQL statements into this code ?!?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace MySqlTest
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //Open SQL File
            using (SqlConnection conn = SqlHelper.GetConn())
            {
                // Use the connection <<< How ?!?!?
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            //Insert Record Into  SQL File

        }

        private void button3_Click(object sender, EventArgs e)
        {
            //Read Record From SQL File

        }

        private void button4_Click(object sender, EventArgs e)
        {
            //Read All Records From SQL File

        }

        private void button5_Click(object sender, EventArgs e)
        {
            //Delete Record From DQL File
        }

        private void button6_Click(object sender, EventArgs e)
        {
            //Close SQL File
        }

        private void button7_Click(object sender, EventArgs e)
        {
            //Quit
            this.Close();
        }

        class SqlHelper
        {
            public static SqlConnection GetConn()
            {
                SqlConnection returnValue = new SqlConnection(@"Data Source=MEDESKTOP;AttachDbFilename=|DataDirectory|\SqlTestDB.mdf;Initial Catalog=MySqlDB;Integrated Security=True");
                returnValue.Open();
                return returnValue;
            }
        }
    }
}

Answer 1

if all you want to do is run an SQL command, use an SQLCommand object. ( MSDN docs here )

here is the sample code from the article...

private static void ReadOrderData(string connectionString)
{
    string queryString = 
        "SELECT OrderID, CustomerID FROM dbo.Orders;";
    using (SqlConnection connection = new SqlConnection(
               connectionString))
    {
        SqlCommand command = new SqlCommand(
            queryString, connection);
        connection.Open();
        SqlDataReader reader = command.ExecuteReader();
        try
        {
            while (reader.Read())
            {
                Console.WriteLine(String.Format("{0}, {1}",
                    reader[0], reader[1]));
            }
        }
        finally
        {
            // Always call Close when done reading.
            reader.Close();
        }
    }
}

things to note:

1. uses a SqlConnection object with a Using block
2. uses an SqlCommand object
3. uses an SqlDataReader object
4. explicitly closes the SqlConnection with finished with it