how can I populate data table with values from a database

Question

I wanted to populate data table with the value taken from the database. I want to use Select condition with the values taken from textbox.. I have written the following code in C#, please tell me whether it is a right approach. It is showing exception about connection string.. but I wanted to know whether my approach is correct or not.. please do comment.

public partial class searchsale : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {

            SqlConnection conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\rdb.mdf;Integrated Security=True;User Instance=True");

            conn.Open();
            string scriptname = TextBox1.Text;
            string accnum = TextBox2.Text;
            string sql = @"select scriptname,accnum,Quantity,price from transac where scriptname = @sn, accnum = @an and transactio = 'Sell'";
            SqlCommand cmd = new SqlCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = sql;
            cmd.Parameters.AddWithValue("@an", accnum);
            cmd.Parameters.AddWithValue("@sn", scriptname);
            SqlDataReader dr = cmd.ExecuteReader();
            DataTable dt = GetDataTable(sql);
        }
        catch (Exception ex)
        {
            Response.Write("error" + ex.ToString());
        }

    }
    private DataTable GetDataTable (string sql)
    {
        DataTable dt = new DataTable();
        using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ToString()))
        {
            SqlDataAdapter da = new SqlDataAdapter(sql, conn);
            da.Fill(dt);
        }
        return dt;
    }
}

Answer 1

The error with your code is because you have not set the connection property of your command .

and for using data table the most simple way is using :

try
{
    var connection = @"your connection string";
    //your command
    var command = "your command";
    var dataAdapter = new System.Data.SqlClient.SqlDataAdapter(command, connection);
    var dataTable = new DataTable();

    //Get data
    dataAdapter.Fill(dataTable);
}
catch (System.Data.SqlClient.SqlException sqlEx)
{
    //Use sqlEx.Number to hanlde excception more specific
    //for example if sqlEx.Number -1 => Could Not Connect to Server.
}
catch (Exception ex)
{
}

Answer 2

Problem is in your below code line for GetDataTable (string sql) method. You will have to use ConnectionString property. I would suggest you to read about ADO.NET more from MSDN.

using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ToString()))
        {

Should be

ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString

It should look like

using (SqlConnection conn = new 
SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
        {

Answer 3

public static class SqlDBHelper
{
    public static DataSet ExecuteDataSet(string sql, CommandType cmdType, params SqlParameter[] parameters)
    {
        using (DataSet ds = new DataSet())
        using (SqlConnection connStr = new SqlConnection(ConfigurationManager.ConnectionStrings["DbConn"].ConnectionString))
        using (SqlCommand cmd = new SqlCommand(sql, connStr))
        {
            cmd.CommandType = cmdType;
            foreach (var item in parameters)
            {
                cmd.Parameters.Add(item);
            }

            try
            {
                cmd.Connection.Open();
                new SqlDataAdapter(cmd).Fill(ds);
            }
            catch (Exception ex)
            {
                throw ex;
            }
            return ds;
        }
    }
}

Answer 4

your code looks right except the connection string. You have declared the connection string at the beginning as

  SqlConnection conn = new SqlConnection(@"Data      Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\rdb.mdf;Integrated Security=True;User Instance=True");

But in your connection initialization it looks like you are getting it from App config file.

using (SqlConnection conn = new  SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ToString()))

So instead of having connection in your code put it in the app config file and remove the connection from your code something like this

     <?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="ConnectionString" 
    connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\rdb.mdf;Integrated Security=True;User Instance=True"/>
  </connectionStrings>
</configuration> 

Thank you,

Birhanu