[C#] 简单的 Helper 封装 -- SQLiteHelper

using System;
using System.Data;
using System.Data.SQLite;

namespace SqliteConsoleApp
{
    /// <summary>
    /// SQLite 助手
    /// </summary>
    public sealed class SQLiteHelper
    {
        private const string ConnectionStr = "Data Source=recipes.s3db";
        private static SQLiteHelper _instance;
        private static readonly object Locker = new object ();

        private SQLiteHelper()
        {
        }

        /// <summary>
        /// 获取实例
        /// </summary>
        /// <returns></returns>
        public static SQLiteHelper GetInstance()
        {
            if (_instance == null )
            {
                lock (Locker)
                {
                    if (_instance == null )
                    {
                        _instance = new SQLiteHelper ();
                    }
                }
            }

            return _instance;
        }

        /// <summary>
        /// 获取数据表
        /// </summary>
        /// <param name="cmdText"> 需要执行的命令文本 </param>
        /// <returns> 一个数据表集合 </returns>
        public DataTable GetDataTable( string cmdText)
        {
            var dt = new DataTable();

            try
            {
                using (var conn = new SQLiteConnection (ConnectionStr))
                {
                    conn.Open();
                    var cmd = new SQLiteCommand(conn) {CommandText = cmdText};
                    using (var reader = cmd.ExecuteReader())
                    {
                        dt.Load(reader);
                    }
                }
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }

            return dt;
        }

        /// <summary>
        /// 执行非查询命令
        /// </summary>
        /// <param name="cmdText"> 需要执行的命令文本 </param>
        /// <returns> 返回更新的行数 </returns>
        public int ExecuteNonQuery( string cmdText)
        {
            using (var conn = new SQLiteConnection (ConnectionStr))
            {
                conn.Open();
                var cmd = new SQLiteCommand(conn) {CommandText = cmdText};
                var rowsUpdated = cmd.ExecuteNonQuery();

                return rowsUpdated;
            }
        }

        /// <summary>
        /// 执行检索单项命令
        /// </summary>
        /// <param name="cmdText"> 需要执行的命令文本 </param>
        /// <returns> 一个字符串 </returns>
        public string ExecuteScalar( string cmdText)
        {
            using (var conn = new SQLiteConnection (ConnectionStr))
            {
                conn.Open();
                var cmd = new SQLiteCommand(conn) {CommandText = cmdText};
                var value = cmd.ExecuteScalar();

                if (value != null )
                {
                    return value.ToString();
                }
            }

            return "" ;
        }
    }
}