CSharp: Lazy Load Pattern in donet core 6

 

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using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;   namespace Geovin.Du.DuLazyLoad.DuGhosts {       /// <summary>     /// Lazy Load Pattern     /// </summary>     public enum LoadStatus     {         /// <summary>         /// 无加载         /// </summary>         Unloaded,         /// <summary>         /// 正加哉         /// </summary>         Loading,         /// <summary>         /// 已加载         /// </summary>         Loaded,     }   }     using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;   namespace Geovin.Du.DuLazyLoad.DuGhosts {       /// <summary>     /// Lazy Load Pattern     /// </summary>     public class GhostCollege : DomainObject     {         private string? _missionStatement;         private int? _numberOfStudents;         private Library? _library;         /// <summary>         ///         /// </summary>         /// <param name="id"></param>         public GhostCollege(int id)             : base(id)         {             Id = id;             Console.WriteLine("学院初始化完成.");         }         /// <summary>         ///         /// </summary>         public string MissionStatement         {             get             {                 LoadIfNecessary();                 return _missionStatement!;             }             set => _missionStatement = value;         }         /// <summary>         ///         /// </summary>         public int NumberOfStudents         {             get             {                 LoadIfNecessary();                 return _numberOfStudents!.Value;             }             set => _numberOfStudents = value;         }         /// <summary>         ///         /// </summary>         public Library Library         {             get             {                 LoadIfNecessary();                 return _library!;             }             set => _library = value;         }         /// <summary>         ///         /// </summary>         public void ShowDetails() =>             Console.WriteLine(                 $"大学的使命是: '{MissionStatement}'.\n" +                 $"这所学院图书馆拥有藏书 {Library.NumberOfBooks} 册， " +                 $"成立于 {Library.EstablishmentDate.ToShortDateString()}.");         /// <summary>         ///         /// </summary>         /// <returns></returns>         protected override object[] FetchData() =>             new object[3]             {             "学习、发现、治愈、创造，让世界变得更美好",             850,             new Library(),             };         /// <summary>         ///         /// </summary>         /// <param name="dataRow"></param>         protected override void ApplyLoadedData(object[] dataRow)         {             Console.WriteLine("数据加载中...");               _missionStatement = (string)dataRow[0];             _numberOfStudents = (int)dataRow[1];             _library = (Library)dataRow[2];         }     }   }     using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;   namespace Geovin.Du.DuLazyLoad.DuGhosts {       /// <summary>     /// Lazy Load Pattern     /// </summary>     public abstract class DomainObject     {         private LoadStatus _status;         /// <summary>         ///         /// </summary>         /// <param name="id"></param>         protected DomainObject(int id)         {             Id = id;         }           public int Id { get; init; }         public bool IsGhost => _status == LoadStatus.Unloaded;         public bool IsLoaded => _status == LoadStatus.Loaded;           /// <summary>         /// Note template method pattern.         /// </summary>         public virtual void LoadIfNecessary()         {             if (!IsGhost)             {                 return;             }               var dataRow = FetchData();               MarkAsLoading();             ApplyLoadedData(dataRow);             MarkAsLoaded();         }         /// <summary>         ///         /// </summary>         /// <returns></returns>         protected abstract object[] FetchData();         /// <summary>         ///         /// </summary>         /// <param name="dataRow"></param>         protected abstract void ApplyLoadedData(object[] dataRow);         /// <summary>         ///         /// </summary>         private void MarkAsLoading() => _status = LoadStatus.Loading;         /// <summary>         ///         /// </summary>         private void MarkAsLoaded() => _status = LoadStatus.Loaded;     }   }   using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;   namespace Geovin.Du.DuLazyLoad.DuGhosts {       /// <summary>     /// Lazy Load Pattern     /// </summary>     public class CollegeFactory     {           /// <summary>         ///         /// </summary>         /// <param name="id"></param>         /// <returns></returns>         public GhostCollege CreateFromId(int id) => new(id);     }   }   using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using Geovin.Du.BuildingBlocks;     namespace Geovin.Du.DuLazyLoad.DuGhosts {       /// <summary>     /// Lazy Load Pattern     /// </summary>     public static class GhostsExecutor     {           /// <summary>         ///         /// </summary>         public static void Execute()         {             ConsoleExtension.WriteSeparator("Lazy Load Pattern：Ghosts demo");               var collegeFactory = new CollegeFactory();             var college = collegeFactory.CreateFromId(1);               // College library shouldn't have been constructed before calling ShowDetails method.             Console.WriteLine("给我更多关于这所大学的细节!");             college.ShowDetails();               Console.WriteLine("\n给我更多关于这所大学的细节!");             college.ShowDetails();         }     } }

　　

调用：

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1	Geovin.Du.DuLazyLoad.DuGhosts.GhostsExecutor.Execute();

　　

输出：

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Lazy Load Pattern：Ghosts demo -------------------------------------------------- 学院初始化完成. 给我更多关于这所大学的细节! 加载库... 数据加载中... 大学的使命是: '学习、发现、治愈、创造，让世界变得更美好'. 这所学院图书馆拥有藏210000册 ，成立于 2008/5/28.   给我更多关于这所大学的细节! 大学的使命是: '学习、发现、治愈、创造，让世界变得更美好'. 这所学院拥有图书馆210000 书 和 成立于 2008/5/28.