N-Tier Architecture

Form User Interface:

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using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace WinFormAppN_TierArchitecture.BLL

{

   public class EmployeeHelper

   {

      public static void SaveErrorLog(Exception ex)

      {

         string fileName = Environment.CurrentDirectory + "\\ERROR_" + Guid.NewGuid() + ".txt";

         File.WriteAllText(fileName, ex.ToString());

      }

   }

}

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using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace WinFormAppN_TierArchitecture.BLL

{

   public static class EmployeeConverter

   {

      #region [ ToDecimal ]

      public static Decimal ToDecimal(object value)

      {

         return ToDecimal(value, 0);

      }

      private static Decimal ToDecimal(object value, decimal defaultValue)

      {

         decimal retVal = defaultValue;

         if (value.Assigned())

         {

            Decimal.TryParse(Convert.ToString(value), out retVal);

         }

         return retVal;

      }

      #endregion

      #region [ ToInt32 ]

      public static Int32 ToInt32(object value, Int32 defaultValue)

      {

         Int32 retVal = defaultValue;

         if (value.Assigned())

         {

            Int32.TryParse(Convert.ToString(value), out retVal);

         }

         return retVal;

      }

      public static Int32 ToInt32(object value)

      {

         return ToInt32(value, 0);

      }

      #endregion

      public static bool Assigned(this object o)

      {

         if (o is string)

            return !string.IsNullOrEmpty((string)o);

         if (o is DateTime)

            return (DateTime)o > DateTime.MinValue;

         return (o != null);

      }

   }

}

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using System;

using System.Collections.Generic;

using System.Data;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using WinFormAppN_TierArchitecture.DAL;

namespace WinFormAppN_TierArchitecture.BLL

{

   public class EmployeeBLL

   {

      public DataTable GetEmployees()

      {

         try

         {

            EmployeeDAL empDAL = new EmployeeDAL();

            return empDAL.GetEmployees();

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

      }

      public DataTable GetEmployee(int EmployeeId)

      {

         try

         {

            EmployeeDAL empDAL = new EmployeeDAL();

            return empDAL.GetEmployee(EmployeeId);

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

      }

   }

}

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using System;

using System.Collections.Generic;

using System.Data;

using System.Data.SqlClient;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using WinFormAppN_TierArchitecture.BLL;

namespace WinFormAppN_TierArchitecture.DAL

{

   public class EmployeeDAL

   {

      public string connectionString = "Data Source=NURHAK-KAYA;Initial Catalog=northwind;Integrated Security=True";

      SqlConnection con = new SqlConnection();

      DataTable dt = new DataTable();

      public DataTable GetEmployees()

      {

         try

         {

            con.ConnectionString = connectionString;

            if (con.State == ConnectionState.Closed)

               con.Open();

            SqlCommand cmd = new SqlCommand("select * from Employees", con);

            SqlDataReader rd = cmd.ExecuteReader();

            dt.Load(rd);

            return dt;

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

      }

      public DataTable GetEmployee(int EmployeeId)

      {

         try

         {

            con.ConnectionString = connectionString;

            if (con.State == ConnectionState.Closed)

               con.Open();

            SqlCommand cmd = new SqlCommand("select * from Employees where EmployeeID=" + EmployeeId, con);

            SqlDataReader rd = cmd.ExecuteReader();

            dt.Load(rd);

            return dt;

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

     }

   }

}

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using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

using WinFormAppN_TierArchitecture.BLL;

namespace WinFormAppN_TierArchitecture

{

   public partial class Form1 : Form

   {

      public Form1()

      {

         InitializeComponent();

      }

      private void Form1_Load(object sender, EventArgs e)

      {

         try

         {

            EmployeeBLL empBLL = new EmployeeBLL();

            this.dataGridView1.DataSource = empBLL.GetEmployees();

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

      }

      private void button1_Click(object sender, EventArgs e)

      {

         try

         {

            EmployeeBLL empBLL = new EmployeeBLL();

            int employeeId = EmployeeConverter.ToInt32(this.textBox1.Text);

            this.dataGridView1.DataSource = empBLL.GetEmployee(employeeId);

         }

         catch (Exception ex)

         {

            EmployeeHelper.SaveErrorLog(ex);

            throw;

         }

      }

   }

}

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Architecture:

Get All Employees List:

Get One Employee By EmployeeId: