[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 "" ;
         }
     }
 }