Windows Forms: Insert Update Delete View data in SQL Server using 3 Tiers in C#

Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "EF3Tiers" and then click OK

Select Class Library, then create DataLayer, Model and BusinessLayer project

Step 2: Design your form as below

Form1

frmAddEditContact

Step 3: Create an EF model as below

You should create a Contact table with fileds corespond the contact class

Step 4: Add an interface to DataLayer project

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Model;

namespace DataLayer
{
    public interface IContactRepository
    {
        List<Contact> GetAll();
        Contact GetById(int id);
        Contact Insert(Contact obj);
        void Update(Contact obj);
        void Delete(Contact obj);
    }
}

Create a ContactRepository class to handle access database

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Model;

namespace DataLayer
{
    public class ContactRepository : IContactRepository
    {
        public void Delete(Contact obj)
        {
            using(ContactEntities db = new ContactEntities())
            {
                db.Contacts.Attach(obj);
                db.Contacts.Remove(obj);
                db.SaveChanges();
            }
        }

        public List<Contact> GetAll()
        {
            using (ContactEntities db = new ContactEntities())
            {
                return db.Contacts.ToList();
            }
        }

        public Contact GetById(int id)
        {
            using (ContactEntities db = new ContactEntities())
            {
                return db.Contacts.Find(id);
            }
        }

        public Contact Insert(Contact obj)
        {
            using (ContactEntities db = new ContactEntities())
            {
                db.Contacts.Add(obj);
                db.SaveChanges();
                return obj;
            }
        }

        public void Update(Contact obj)
        {
            using (ContactEntities db = new ContactEntities())
            {
                db.Contacts.Attach(obj);
                db.Entry(obj).State = System.Data.Entity.EntityState.Modified;
                db.SaveChanges();
            }
        }
    }
}

Step 5: Add a ContactServices to BusinessLayer project

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using DataLayer;
using Model;

namespace BusinessLayer
{
    public static class ContactServices
    {
        static IContactRepository repository;

        static ContactServices()
        {
            repository = new ContactRepository();
        }

        public static List<Contact> GetAll()
        {
            return repository.GetAll();
        }

        public static Contact GetById(int id)
        {
            return repository.GetById(id);
        }

        public static Contact Insert(Contact obj)
        {
            return repository.Insert(obj);
        }

        public static void Update(Contact obj)
        {
            repository.Update(obj);
        }

        public static void Delete(Contact obj)
        {
            repository.Delete(obj);
        }
    }
}

You can easily change code in business layer, don't need modify code in UI

Step 6: Add code to handle your form as below

Form1

using BusinessLayer;
using Model;
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;

namespace EF3Tiers
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Call business layer to get data
            contactBindingSource.DataSource = ContactServices.GetAll();
        }

        private void btnAdd_Click(object sender, EventArgs e)
        {
            using(frmAddEditContact frm =new frmAddEditContact(null))
            {
                if (frm.ShowDialog() == DialogResult.OK)
                    contactBindingSource.DataSource = ContactServices.GetAll();
            }
        }

        private void btnEdit_Click(object sender, EventArgs e)
        {
            if (contactBindingSource.Current == null)
                return;
            using (frmAddEditContact frm = new frmAddEditContact(contactBindingSource.Current as Contact))
            {
                if (frm.ShowDialog() == DialogResult.OK)
                    contactBindingSource.DataSource = ContactServices.GetAll();
            }
        }

        private void btnDelete_Click(object sender, EventArgs e)
        {
            if (contactBindingSource.Current == null)
                return;
            if(MessageBox.Show("Are you sure want to delete this record ?", "Message", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
            {
                ContactServices.Delete(contactBindingSource.Current as Contact);
                contactBindingSource.RemoveCurrent();
            }
        }
    }
}

frmAddEditContact

using BusinessLayer;
using Model;
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;

namespace EF3Tiers
{
    public partial class frmAddEditContact : Form
    {
        bool IsNew;
        public frmAddEditContact(Contact obj)
        {
            InitializeComponent();
            if (obj == null)
            {
                contactBindingSource.DataSource = new Contact();
                IsNew = true;
            }
            else
            {
                contactBindingSource.DataSource = obj;
                IsNew = false;
            }
        }

        private void frmAddEditContact_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (DialogResult == DialogResult.OK)
            {
                if (string.IsNullOrEmpty(txtContactName.Text))
                {
                    MessageBox.Show("Please enter your contact name.", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    txtContactName.Focus();
                    e.Cancel = true;
                    return;
                }
                if (IsNew)
                    ContactServices.Insert(contactBindingSource.Current as Contact);
                else
                    ContactServices.Update(contactBindingSource.Current as Contact);
            }           
        }
    }
}

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