I use the entitiy framwork code first method, How can I display the last riff number in the database by clicking the Add text box?, my textbox code is key (int).

Question

Answer 1

Here is an example that has a table as follows

Form interface

Using EF Core 5 and a custom BindingList which allows the DataGridView to be sortable (not needed for your question but nice and if you want it I can post the source)

using System;  
using System.Data;  
using System.Linq;  
using System.Windows.Forms;  
using WindowsFormsApp1.Classes;  
using WindowsFormsApp1.Data;  
using WindowsFormsApp1.Models;  
  
namespace WindowsFormsApp1  
{  
    /// <summary>  
    /// C# 9  
    /// </summary>  
    public partial class Form1 : Form  
    {  
        private readonly BindingSource _bindingSource = new ();  
          
        /// <summary>  
        /// Custom BindingList to allow the DataGridView to be sortable  
        /// </summary>  
        private SortableBindingList<Country> _countryBindingList;  
        public Form1()  
        {  
            InitializeComponent();  
              
            Shown += OnShown;  
        }  
  
        private void OnShown(object? sender, EventArgs e)  
        {  
            using var context = new Context();  
              
            _countryBindingList = new SortableBindingList<Country>(context.Country.ToList());  
            _bindingSource.DataSource = _countryBindingList;  
              
            dataGridView1.DataSource = _bindingSource;  
        }  
  
        private void LastIdButton_Click(object sender, EventArgs e)  
        {  
            using var context = new Context();  
              
            /*  
             * If no record, add one with a default value for a country name,  
             * in reality this would need input from the user e.g. a ComboBox  
             * selection  
             */  
            if (!context.Country.Any())  
            {  
                Country newCountry = new Country() {Name = "TODO"};  
                context.Country.Add(newCountry);  
                context.SaveChanges();  
                LastIdTextBox.Text = newCountry.Id.ToString();  
                NextIdTextBox.Text = (newCountry.Id + 1).ToString();  
            }  
            /*  
             * We have at least one record, get the last record  
             * From the last record get the key, id and display  
             * the current last id and another text box the last id  
             * plus one.  
             */  
            else  
            {  
                Country country = context.Country.OrderBy(countryItem => countryItem.Id).LastOrDefault();  
                LastIdTextBox.Text = country.Id.ToString();  
                NextIdTextBox.Text = (country.Id + 1).ToString();  
            }  
        }  
    }  
}  
  

In regards to the custom BindingList, to get the current record in the DataGridView

var currentCountry = _countryBindingList[_bindingSource.Position];