Hi Experts I am new to C#. I have a Form that add new a customer . But I want to check if that customer already exist. How do I do it from the the code shown here below. Thanks
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;
using DevExpress.XtraBars.Alerter;
using DevExpress.XtraEditors;
using MakGarm.Business;
using MakGarm.Business.Contracts;
using MakGarm.Common.Entities.Core;
using MakGarm.Common.Entities.GeneralLedgerAccounts;
using MakGarm.Common.Entities.Miscellaneous;
using MakGarm.Common.Entities.SubsidiaryLedgerAccounts;
using Microsoft.Practices.Unity;
using Uwapi.Utils;
 
namespace MakGarm.Start.Customers {
 
    public partial class frmAddCustomer : DevExpress.XtraEditors.XtraForm {
 
        private readonly ICustomerService _customerService;
 
        private readonly Customer _customer;
        private readonly IContactService _contactService;
 
        
        private readonly IFinancialMonthService _financialMonthService;
        private readonly FinancialYear _financialYear;
 
        public int NewcontactId;
        public int CheckCustomerId;
 
        public frmAddCustomer() {
            InitializeComponent();
 
            _customerService = UnityConfig.GetContainer().Resolve<ICustomerService>();
            _contactService = UnityConfig.GetContainer().Resolve<IContactService>();
            _financialMonthService = UnityConfig.GetContainer().Resolve<IFinancialMonthService>();
 
            _customer = new Customer() {
                Active = true,
                Accountclosed = false,
                Datecreated = DateTime.Now,
                CreditDays = 0,
                CreditLimit = 0,
                LastEditedDate = DateTime.Now,
                CompanyBranchId = CurrentUserInfo.User.CompanyBranch.CompanyId,
                CheckerUserId = CurrentUserInfo.User.UserId,
                LastEditorUserId = CurrentUserInfo.User.UserId,
            };
        }
 
        private void frmAddCustomer_Load(object sender, EventArgs e){
 
            customerBindingSource.DataSource = _customer;
            ContactBindingSource.DataSource = _contactService.GetAll();
            FinacialMonthsbindingSource.DataSource = _financialMonthService.GetCurrentFinancialMonth();
        }
 
        private void simpleButtonAcccept_Click(object sender, EventArgs e){
 
            _customer.ContactId = NewcontactId;
            _customer.BillingStartFinancialMonthId = _financialMonthService.GetCurrentFinancialMonth().FinancialMonthId;
 
           
            customerBindingSource.EndEdit();
            _customerService.Insert(_customer);
 
 
            AlertButton Btn = new AlertButton();
            Btn.Hint = "Open File";
            Btn.Name = "Button Open";
            alertControl1.Buttons.Add(Btn);
            alertControl1.ButtonClick += new AlertButtonClickEventHandler(alertControl1_ButtonClick);
           AlertInfo info = new AlertInfo("GMIS 2015 Alert",
                "The new job card record has been Added successfully");
            alertControl1.Show(this, info);
 
            this.Close();
 
        }
 
 
        private void alertControl1_ButtonClick(object sender, AlertButtonClickEventArgs e) {
            throw new NotImplementedException();
        }
        private void contactNameSearchLookUpEdit_EditValueChanged(object sender, EventArgs e){
            var selectedContact = contactNameSearchLookUpEditView.GetFocusedRow() as Contact;
            if (selectedContact == null) return;
            NewcontactId = selectedContact.ContactId;
        }
 
 
        private void simpleButtonCancel_Click(object sender, EventArgs e) {
            if(MessageBox.Show("Do you really want to cancel this process","GMIS - Cancel",MessageBoxButtons.YesNo,MessageBoxIcon.Question)==DialogResult.Yes) {
                contactNameSearchLookUpEdit.Text = string.Empty;
                remarksMemoEdit.Text = string.Empty;
            }
        }
 
 
        private void simpleButtonClose_Click(object sender, EventArgs e) {
 
            if (MessageBox.Show("Are You sure", "GMIS - Close", MessageBoxButtons.YesNo, MessageBoxIcon.Question) ==
                DialogResult.Yes) {
                this.Close();
            }
 
        }
    }
}