Question

I’m learning about classes in C# and am trying to build a “DataAccessClass”. I have a working “OpenSqlConnection” void and am using it as a guide to build a “OpenSqlDatareader” void. I am attempting to consolidate all my database calls in this class. My boggle is how to pass a DataTable from the class to the aspx page to bind it with a ListView. I have been reading and trying for a day to make this work and cannot figure out what I am doing wrong…

Here’s the Page_Load:

// --------------------------------------------------------------------------------
// Populate the Customers page.
// --------------------------------------------------------------------------------


// Define the query
string sqlQuery = " SELECT CustomerID, LastName + ', ' + FirstName AS CustomerName, Email, City, State, Phone"
                            + " FROM Customer"
                            + " ORDER BY LastName, FirstName";

string strErrorMessage = "";

if (DataAccessClass.OpenSqlConnection(out strErrorMessage) == false)
{
    string strErrorType = "Database Connection Error:";
    SendErrorMessageToClient(strErrorType, strErrorMessage);
}

else if (DataAccessClass.OpenSqlDatareader(sqlQuery, out dt, out strErrorMessage) == false)
{
    string strErrorType = "Datareader Error:";
    SendErrorMessageToClient(strErrorType, strErrorMessage);
}

else

{
    // Bind the Listview
    lvCustomers.DataSource = dt;
    lvCustomers.DataBind();
    dt.Dispose();
}

And here’s the class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;

/// <summary>
/// Summary description for DataAccessClass
/// </summary>
/// 
public class DataAccessClass
{
    public DataAccessClass()
{
    //
    // TODO: Add constructor logic here
    //
}



// -----------------------------------------------------------------------------------------
// Name: OpenSqlConnection
// Abstract: Open a connection to a SQL Server
// -----------------------------------------------------------------------------------------
public static bool OpenSqlConnection(out string strErrorMessage)
{

    SqlConnection theConnection = new SqlConnection();
    bool blnResult = false;
    string strConnectionString = ConfigurationManager.ConnectionStrings["MyConn"].ConnectionString;
    strErrorMessage = "";

    if (theConnection == null)
        theConnection = new SqlConnection();

    try
    {
        switch (theConnection.State)
        {
            case ConnectionState.Broken:
                theConnection.Close();
                theConnection.ConnectionString = strConnectionString;
                theConnection.Open();
                blnResult = true;
                break;

            case ConnectionState.Closed:
                theConnection.ConnectionString = strConnectionString;
                theConnection.Open();
                blnResult = true;
                break;

            case ConnectionState.Open:
                blnResult = true;
                break;

            default:
                strErrorMessage = "Connection state is " + theConnection.State.ToString();
                break;
        }
    }
    catch (Exception excError)
    {
        strErrorMessage = excError.Message;
    }

    return blnResult;
}

// -----------------------------------------------------------------------------------------
// Name: OpenSqlDataReader
// Abstract: Open a SQL DataReader
// -----------------------------------------------------------------------------------------
public static bool OpenSqlDatareader(string sqlQuery, out dt, out string strErrorMessage)
{

    SqlConnection theConnection = new SqlConnection();

    bool blnResult = false;
    string strConnectionString = ConfigurationManager.ConnectionStrings["MyConn"].ConnectionString;
    strErrorMessage = "";

    if (theConnection == null)
        theConnection = new SqlConnection();

    try
    {
        // Declare a SQL Adapter
        SqlDataAdapter da = new SqlDataAdapter(sqlQuery, theConnection);

        // Declare a DataTable
        DataTable dt = new DataTable();

        // Populate the DataTable
        da.Fill(dt);

        // Clean up.
        dt.Dispose();
        da.Dispose();
        theConnection.Close();
    }
    catch (Exception excError)
    {
        strErrorMessage = excError.Message;
    }

    return blnResult;
  }
}

The error message is: “The type or namespace name ‘dt’ could not be found (are you missing a using directive or an assembly reference?)”
Any suggestions?

Answer 1

before calling OpenSqlDatareader you need to declare dt

DataTable dt;// no need to assign 

....
else if (DataAccessClass.OpenSqlDatareader(sqlQuery, out dt, out strErrorMessage) == false)
{
    string strErrorType = "Datareader Error:";
    SendErrorMessageToClient(strErrorType, strErrorMessage);
}
...

change your signature of OpenSqlDatareader with out DataTable dt

public static bool OpenSqlDatareader(string sqlQuery, out DataTable dt, out string strErrorMessage)

inside the method

// create new  DataTable
dt = new DataTable();