Login system demonstrating 3-tier architecture and connect to IBM DB2

Introduction

The article demonstrates how to develop applications using multiple tiers and connect an IBM DB2 database to your .NET application. The 3-tier architecture is usually known to have:

1. Client Layer (GUI)
2. Business Application Layer (Logic and Validations)
3. Data Access Layer (queries /stored procedures)

The client layer will be in a separate project, and the rest of the layers will be created in your class library project (optional).

Adding a Class Library (App_Code_Library) to the Client Side (Contact_System)

Next will show you how to add references to your Class Library (App_Code_Library) to your Client Side (Contact_System). The references will be the” .DLL” files usually located in the bin>debug folder.

By doing this, it allows you to call the public classes from your Class Library (App_Code_Library) and use them in your client side.

Right click References >Add References> Browse> App_Code_Library>Bin>Debug> App_Code_Library.dll.

Adding IBM DB2.Data.dll file to your Client Side (Contact_System) .

This allows you to be able to use classes like DB2Connection, DB2Command, DB2DataReader etc.

Right click References >Add References> .NET > .Data.DB2>.

In the end your solutions should have the .dll files showed in the picture below.

Using the code

Client Side (UI)

Client-side backend code (sign in) button

using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using App_Code_Library.Business_Application;
//Reference Logic Layer to get Classes like CredantialsBAL and their methods

namespace Contact_System
{
    /// <summary>
    /// Interaction logic for signin.xaml
    /// </summary>
    public partial class signin : Window
    {
        public signin()
        {
            InitializeComponent();
            txtUsername.Focus();
        }

        private void btnSignin_Click(object sender, RoutedEventArgs e)//event to sign in
        {
            CredantialsBAL credantials = new CredantialsBAL();
            bool found = credantials.authenticate(txtUsername.Text, txtuserID.Password);
            if (found)//user exist
            {
                Phonebook goPhonebook = new Phonebook(credantials.userID);
                this.Hide();
                goPhonebook.ShowDialog();
            }
            else if (!found)//user does not Exist
            {
                MessageBox.Show("Oops! Incorrect login details", "Contact System:Error", 
                  MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
    }
}

Business Layer (Logic Layer)

using System.Data;
using System.Windows.Forms;
using App_Code_Library.Data_Access;
//Reference your Data Access Layer to get classes like CredantialsDAL

namespace App_Code_Library.Business_Application
{
    public class CredantialsBAL
    {
        public string userID;
        public  bool  authenticate(string username, string password)
        {
            CredantialsDAL dal = new Data_Access.CredantialsDAL();
            DataTable dTable = dal.getAuthentication();

            bool found = false;
            foreach (DataRow dRow in dTable.Rows)
            {
                if ((username == dRow["_username"].ToString()) && 
                             password == dRow["_password"].ToString())
                {
                    userID = dRow["userID"].ToString();
                    found = true;
                }
            }
            if 
                (!found)
            {
                return false;
            }

            return found;
           
        }    
    }
}

Data Access Layer (Queries/Stored Procedures)

using System.Linq;
using System.Text;
using System.Data;
using IBM.Data.DB2;//Add this line to refrence DB2 Classes

namespace App_Code_Library.Data_Access
{
    public class CredantialsDAL
    {
        // Your connection string to connect IBM DB2 Database 
        string connString = "Database=DBPBOOK;userID=db2admin;password=mypassword;server=localhost";

        #region Check user Exist
        public DataTable getAuthentication()
        {

            using (DB2Connection con = new DB2Connection(connString))
            {
                DB2Command cmd = new DB2Command("SELECT * FROM YourSchemaName.tbl_credantials", con);
                DataTable dTable = new DataTable();
                DB2DataAdapter adapter = new DB2DataAdapter(cmd);
                adapter.SelectCommand = cmd;
                adapter.Fill(dTable);

                return dTable;
            }
        }
        #endregion
    }
}

References

• 3-Tier Architecture in ASP.NET with C#: By SheoNarayan.