r1.cs

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

namespace BLL
{
    public class BillBLL
    {
        private BillDAL dal = new BillDAL();

		public BindingList<Bill> FetchAll()
		{
			BindingList<Bill> list = new BindingList<Bill>();

			var dalCollection = dal.FetchAll();
		
			foreach (var dalObject in dalCollection)
			{
                Bill bill = new Bill();
				bill.LoadFromDB(dalObject);
			    list.Add(bill);					
				
            }

			return list;
		}
		
		public Bill Fetch(int id)
		{
			Bill bill = null;
			var dalObject = dal.Fetch(id);
			if (dalObject != null)
			{
				bill = new Bill();
				bill.LoadFromDB(dalObject);
			}
			return bill;
			
		}

        public BindingList<Bill> FetchWithContractId(int id)
        {
            BindingList<Bill> bills = new BindingList<Bill>();
            foreach (var dalObject in dal.FetchAll())
            {
                var bill = new Bill();
                bill.LoadFromDB(dalObject);
                if (bill.ContractId == id)
                {
                    bills.Add(bill);
                }
            }
            return bills;
        }

		public void Insert(Bill a)
		{
			if (string.IsNullOrEmpty(a.Error))
			{
                dal.Insert(a.Id, a.ContractId, a.DateIssued, a.PaymentDeadline,  a.Discount, a.Paid);
			}
			else
			{
				throw new Exception("Validacija neuspješna: " + a.Error);
			}
		}

		public void Delete(Bill a)
		{
			dal.Delete(a.Id);
		}

		public void Update(Bill a)
		{
			if (string.IsNullOrEmpty(a.Error))
			{
                dal.Update(a.Id, a.ContractId, a.DateIssued, a.PaymentDeadline, a.Discount, a.Paid);
			}
			else
			{
				throw new Exception("Validacija neuspješna: " + a.Error);
			}
		}

		public void RefreshBill(object datasource, int position, object current)
		{
			BindingList<Bill> list = (BindingList<Bill>)datasource;
			Bill a = list[position];
			list[position] = Fetch(a.Id);
		}
	}
}

r2.cs

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

namespace Model
{
    public class BillDAL
    {
        public List<Bill> FetchAll()
		{
			using (RPPP14Entities ctx = new RPPP14Entities())
			{
                return ctx.Bills.ToList();
			}
		}

        public Bill Fetch(int billId)
		{
			using (RPPP14Entities ctx = new RPPP14Entities())
			{
                return ctx.Bills.Where(a => a.Id == billId).SingleOrDefault();
			}
		}

        public void Insert(int id, int contractId, DateTime dateIssued, DateTime? paymentDeadline, decimal? discount, bool paid)
		{
			using (RPPP14Entities ctx = new RPPP14Entities())
			{
				Bill a = new Bill();
				a.Id = id;
                a.ContractId = contractId;
                a.DateIssued = dateIssued;
                a.PaymentDeadline = paymentDeadline;
                a.Discount = discount;
                a.Paid = paid;

                ctx.Bills.Add(a);
				ctx.SaveChanges();
			}			
		}


		public void Update(int id, int contractId, DateTime dateIssued, DateTime? paymentDeadline, decimal? discount, bool paid)
        {
			using (RPPP14Entities ctx = new RPPP14Entities())
			{
				Bill a = ctx.Bills.Where(c => c.Id == id).Single();
    
                a.ContractId = contractId;
                a.DateIssued = dateIssued;
                a.PaymentDeadline = paymentDeadline;
                a.Discount = discount;
                a.Paid = paid;
			
				ctx.SaveChanges();
			}
		}


		public void Delete(int id)
		{
			using (RPPP14Entities ctx = new RPPP14Entities())
			{
				Bill a = ctx.Bills.Where(c => c.Id == id).Single();
                ctx.Bills.Remove(a);
				ctx.SaveChanges();
			}
		}
    }
}