Лістинг програми (TClients)
public class TClients
    {
        [Key]
        public int IDClient { get; set; }
        public string Surname { get; set; }
        public string GivenName { get; set; }
        public string Patronymic { get; set; }
        public string PassportId { get; set; }
        public virtual ICollection<TCredits> CreditT { get; set; }
        public virtual ICollection<TDeposits> DepositsT { get; set; }
    }
Лістинг програми (TCredits)
    public class TCredits
    {
        [Key]
        public int IDCredit { get; set; }
        public int? ClientID { get; set; }
        [ForeignKey("ClientID")]
        public TClients TClients { get; set; }
        public decimal AmoutCredit { get; set; }
        public decimal Percentage { get; set; }
        public DateTime DateOfIssue { get; set; }
        public DateTime RepaymentDate { get; set; }
    }
Лістинг програми (TDeposits)
    public class TDeposits
    {
        [Key]
        public int IDDeposit { get; set; }
        public int? ClientID { get; set; }
        [ForeignKey("ClientID")]
        public TClients TClients { get; set; }
        public string AccountNumber { get; set; }
        public decimal AmountDeposit { get; set; }
        public DateTime StartDate { get; set; }
        public DateTime EndDate { get; set; }
    }
Лістинг програми (ApplicationContext)
public class ApplicationContext : DbContext
    {
        public DbSet<TClients> Clients { get; set; }
        public DbSet<TCredits> Credits { get; set; }
        public DbSet<TDeposits> Deposits { get; set; }

        public ApplicationContext()
        {
            try
            {
                //Database.EnsureDeleted();
                Database.EnsureCreated();
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=BankDB;Trusted_Connection=True;");
        }
Лістинг програми (MainWindow)
public partial class MainWindow : Window
    {
        ApplicationContext db;
        public MainWindow()
        {
            InitializeComponent();
            Load();
        }
        public void Load()
        {
            using (db = new ApplicationContext())
            {
                db.Credits.Load();
                db.Clients.Load();
                db.Deposits.Load();
                dataGridClients.ItemsSource = db.Clients.Local.ToBindingList();
                dataGridCred.ItemsSource = db.Credits.Local.ToBindingList();
                dataGridDep.ItemsSource = db.Deposits.Local.ToBindingList();
            }
        }
        private void btn_Add_Click(object sender, RoutedEventArgs e)
        {

            if (tb_CliSurname.Text != string.Empty || tb_CliGivenName.Text != string.Empty || tb_CliPatronymic.Text != string.Empty || tb_CliPassportId.Text != string.Empty || tb_CredAmoutCredit.Text != string.Empty || tb_CredPercentage.Text != string.Empty || tb_CredDateOfIssue.Text != string.Empty || tb_CredRepaymentDate.Text != string.Empty || tb_DepAccountNumber.Text != string.Empty || tb_DepAmountDeposit.Text != string.Empty || tb_DepStartDate.Text != string.Empty || tb_DepEndDate.Text != string.Empty)
            {
                try
                {
                    using (db = new ApplicationContext())
                    {
                        TClients clients = new TClients
                        {
                            Surname = tb_CliSurname.Text,
                            GivenName = tb_CliGivenName.Text,
                            Patronymic = tb_CliPatronymic.Text,
                            PassportId = tb_CliPassportId.Text
                        };
                        db.Clients.Add(clients);
                        db.SaveChanges();
                        TCredits credits = new TCredits
                        {
                            ClientID = clients.IDClient,
                            AmoutCredit = decimal.Parse(tb_CredAmoutCredit.Text),
                            Percentage = decimal.Parse(tb_CredPercentage.Text),
                            DateOfIssue = DateTime.Parse(tb_CredDateOfIssue.Text),
                            RepaymentDate = DateTime.Parse(tb_CredRepaymentDate.Text)
                        };
                        db.Credits.Add(credits);
                        db.SaveChanges();
                        TDeposits deposits = new TDeposits
                        {
                            ClientID = clients.IDClient,
                            AccountNumber = tb_DepAccountNumber.Text,
                            AmountDeposit = decimal.Parse(tb_DepAmountDeposit.Text),
                            StartDate = DateTime.Parse(tb_DepStartDate.Text),
                            EndDate = DateTime.Parse(tb_DepEndDate.Text)
                        };
                        db.Deposits.Add(deposits);
                        db.SaveChanges();

                        Load();
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
            else
            {
                MessageBox.Show("Будь ласка, введіть дані!", "ПОМИЛКА ВВЕДЕННЯ", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
        private void btn_UpdateDeposit_Click_1(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    int IdDep = (dataGridDep.SelectedItem as TDeposits).IDDeposit;

                    TDeposits updateDep = (from d in db.Deposits
                                             where d.IDDeposit == IdDep
                                             select d).Single();

                    updateDep.ClientID = (dataGridDep.SelectedItem as TDeposits).ClientID;
                    updateDep.AccountNumber = (dataGridDep.SelectedItem as TDeposits).AccountNumber;
                    updateDep.AmountDeposit = (dataGridDep.SelectedItem as TDeposits).AmountDeposit;
                    updateDep.StartDate = (dataGridDep.SelectedItem as TDeposits).StartDate;
                    updateDep.EndDate = (dataGridDep.SelectedItem as TDeposits).EndDate;

                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void btn_UpdateCredit_Click_1(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    int IdCred = (dataGridCred.SelectedItem as TCredits).IDCredit;

                    TCredits updateDep = (from d in db.Credits
                                           where d.IDCredit == IdCred
                                          select d).Single();

                    updateDep.ClientID = (dataGridCred.SelectedItem as TCredits).ClientID;
                    updateDep.AmoutCredit = (dataGridCred.SelectedItem as TCredits).AmoutCredit;
                    updateDep.Percentage = (dataGridCred.SelectedItem as TCredits).Percentage;
                    updateDep.DateOfIssue = (dataGridCred.SelectedItem as TCredits).DateOfIssue;
                    updateDep.RepaymentDate = (dataGridCred.SelectedItem as TCredits).RepaymentDate;

                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void btn_UpdateClient_Click_1(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    int IdCred = (dataGridClients.SelectedItem as TClients).IDClient;

                    TClients updateDep = (from d in db.Clients
                                          where d.IDClient == IdCred
                                          select d).Single();

                    updateDep.Surname = (dataGridClients.SelectedItem as TClients).Surname;
                    updateDep.GivenName = (dataGridClients.SelectedItem as TClients).GivenName;
                    updateDep.Patronymic = (dataGridClients.SelectedItem as TClients).Patronymic;
                    updateDep.PassportId = (dataGridClients.SelectedItem as TClients).PassportId;


                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void btn_DeleteDep_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    TDeposits delDep = new TDeposits() { IDDeposit = int.Parse(tb_DelDep.Text) };
                    db.Deposits.Attach(delDep);
                    db.Deposits.Remove(delDep);
                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void btn_DeleteClient_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    TClients delClient = new TClients() { IDClient = int.Parse(tb_DelClient.Text) };
                    db.Clients.Attach(delClient);
                    db.Clients.Remove(delClient);
                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void btn_DeleteCred_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                using (db = new ApplicationContext())
                {
                    TCredits delCred= new TCredits() { IDCredit = int.Parse(tb_DelCred.Text) };
                    db.Credits.Attach(delCred);
                    db.Credits.Remove(delCred);
                    db.SaveChanges();
                    Load();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }