C# SQLite CRUD example

Form1.cs

using System;
using System.Diagnostics;
using System.IO;
using System.Windows.Forms;
using Microsoft.Data.Sqlite;

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


            CreateDatabaseFile();
            Insert("Ruyut");
            Read();
            Update(1, "Ruyut_1234");
            Read();
            Delete(1);
            Read();
        }


        /// <summary>
        /// 資料庫連接字串
        /// </summary>
        private string _connectionString = "Data Source=db.db;";

        /// <summary>
        /// 建立資料庫檔案
        /// </summary>
        private void CreateDatabaseFile()
        {
            Debug.WriteLine("CreateDatabaseFile");
            if (File.Exists("db.db")) return;
            using (var connection = new SqliteConnection(_connectionString))
            {
                connection.Open();

                var command = connection.CreateCommand();
                command.CommandText =
                    @"CREATE TABLE users (
            	        id	INTEGER,
            	        user_name	TEXT NOT NULL UNIQUE,
                        PRIMARY KEY(id AUTOINCREMENT)
                    );";
                command.ExecuteNonQuery();
            }
        }

        /// <summary>
        /// 新增
        /// </summary>
        /// <param name="userName"></param>
        private void Insert(string userName)
        {
            Debug.WriteLine("Insert");
            using (var connection = new SqliteConnection(_connectionString))
            {
                connection.Open();
                var command = connection.CreateCommand();
                command.CommandText =
                    @"  INSERT INTO users (user_name)
                        values ($userName);
                        select last_insert_rowid();";
                command.Parameters.AddWithValue("$userName", userName);
                int id = Convert.ToInt32((object)command.ExecuteScalar());
                Debug.WriteLine($"\tid = {id}, userName = {userName}");
            }
        }

        /// <summary>
        /// 修改
        /// </summary>
        /// <param name="id"></param>
        /// <param name="userName"></param>
        private void Update(int id, string userName)
        {
            Debug.WriteLine("Update");
            using (var connection = new SqliteConnection(_connectionString))
            {
                connection.Open();
                var command = connection.CreateCommand();
                command.CommandText =
                    @"  UPDATE users
                        SET user_name= $userName
                        WHERE id = $id;";
                command.Parameters.AddWithValue("$userName", userName);
                command.Parameters.AddWithValue("id", id);
                command.ExecuteNonQuery();
            }
        }

        /// <summary>
        /// 刪除
        /// </summary>
        /// <param name="id"></param>
        private void Delete(int id)
        {
            Debug.WriteLine("Delete");
            using (var connection = new SqliteConnection(_connectionString))
            {
                connection.Open();
                var command = connection.CreateCommand();
                command.CommandText =
                    @"  delete from users where id = $id;";
                command.Parameters.AddWithValue("id", id);
                command.ExecuteNonQuery();
            }
        }

        /// <summary>
        /// 查詢、讀取
        /// </summary>
        private void Read()
        {
            Debug.WriteLine("Read");
            using (var connection = new SqliteConnection(_connectionString))
            {
                connection.Open();
                var command = connection.CreateCommand();
                command.CommandText = @"  select * from users";

                using (var reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        var id = reader.GetString(0);
                        var name = reader.GetString(1);

                        Debug.WriteLine($"\tid = {id}, name = {name}");
                    }
                }
            }
        }
    }
}