讨论一下类似BlogEngine内一次性加载所有Post是否可取

时间：2007-12-28 12:27:22 来源：Linux联盟收集整理作者：

试验了一下给BlogEngine生成10000个post 程序第一次运行时等待的时间让我想自杀（白屏了近2分钟)
  看了一下代码，发现BlogEngine在第一次运行时候加载所有Post（从数据库)到List内,类似（Early initialization）
  当新添加post时，给数据库（xml/database)内加入该post同时给List内追加该post
  删除一个post时候从数据库（xml/database)内删除并从List内remove该post
   1
   2private string _Content;
   3/**//// <summary>
   4/// Gets or sets the Content or the post.
   5/// </summary>
   6public string Content
   7{
   8 get
   9 {
   10 if ( _Content == null )
   11 {
   12 _Content = LoadPostContent( this.Id );
   13 }
   14 return _Content;
   15 }
   16 set
   17 {
   18 if ( _Content != value )
   19 MarkDirty( "Content" );
   20 _Content = value;
   21 }
   22}
   23private string LoadPostContent(Guid id)
   24{
   25 string content = null;
   26
   27 string key = string.Format("Be:Content:{0}",id);
   28
   29 // if there is no content cached
   30 object obj = HttpContext.Current.Cache.Get(key);
   31 if(obj == null)
   32 {
   33 // load the post's content from provider here
   34 content = BlogService.LoadPostContent( id );
   35
   36 HttpContext.Current.Cache.Insert(key, content, null, DateTime.Now.AddMinutes(2), TimeSpan.Zero);
   37
   38 // if use xml store the data
   39 // 更丑陋点的 new CacheDependency(_Folder + "posts\\" + id.ToString() + ".xml") in the Cache.Insert Method
   40 }
   41
   42}
   43
   44private static object _SyncRoot = new object();
   45private static List<Post> _Posts;
   46/**//// <summary>
   47/// A sorted collection of all posts in the blog.
   48/// Sorted by date.
   49/// </summary>
   50public static List<Post> Posts
   51{
   52 get
   53 {
   54 lock (_SyncRoot)
   55 {
   56 if (_Posts == null)
   57 {
   58 //in provider the 'FillPosts' method' dose not return the 'real' content' per post；
   59
   60 _Posts = BlogService.FillPosts( );
   61 }
   62 return _Posts;
   63 }
   64 }
   65}
   66
   67in XmlBlogProvider
   68
   69/**//// <summary>
   70/// Retrieves a post based on the specified Id.
   71/// </summary>
   72public override Post SelectPost(Guid id)
   73{
   74 string fileName = _Folder + "posts\\" + id.ToString() + ".xml";
   75 Post post = new Post();
   76 XmlDocument doc = new XmlDocument();
   77 doc.Load(fileName);
   78
   79 post.Title = doc.SelectSingleNode("post/title").InnerText;
   80 post.Description = doc.SelectSingleNode("post/description").InnerText;
   81
   82 post.Content = null; // dose not return the 'real' content'
   83
   84 post.DateCreated = DateTime.Parse(doc.SelectSingleNode("post/pubDate").InnerText);
   85 post.DateModified = DateTime.Parse(doc.SelectSingleNode("post/lastModified").InnerText);
   86
   87 // setting other filed
   88
   89 return post;
   90}
   91Post class in Business object layer
   92
   93private string _Content;
   94/**//// <summary>
   95/// Gets or sets the Content or the post.
   96/// </summary>
   97public string Content
   98{
   99 get
  100 {
  101 if ( _Content == null )
  102 {
  103 _Content = LoadPostContent( this.Id );
  104 }
  105 return _Content;
  106 }
  107 set
  108 {
  109 if ( _Content != value )
  110 MarkDirty( "Content" );
  111 _Content = value;
  112 }
  113}
  114private string LoadPostContent(Guid id)
  115{
  116 string key = string.Format("Be:Content:{0}",id);
  117 string content = null;
  118 // if there is no content cached by id
  119 object obj = HttpContext.Current.Cache.Get(key);
  120 if(obj == null)
  121 {
  122 // load the post's content from provider here
  123 content = BlogService.LoadPostContent( id );
  124
  125 HttpContext.Current.Cache.Insert(key, content, null, DateTime.Now.AddMinutes(2), TimeSpan.Zero);
  126
  127 // if use xml store the data
  128 // we can use a CacheDependency like new CacheDependency(_Folder + "posts\\" + id.ToString() + ".xml") in the Cache.Insert Method
  129
  130 return content;
  131 }
  132 return (strong)obj;
  133
  134}
  135
  136private static object _SyncRoot = new object();
  137private static List<Post> _Posts;
  138/**//// <summary>
  139/// A sorted collection of all posts in the blog.
  140/// Sorted by date.
  141/// </summary>
  142public static List<Post> Posts
  143{
  144 get
  145 {
  146 lock (_SyncRoot)
  147 {
  148 if (_Posts == null)
  149 {
  150 //in provider the 'FillPosts' method' dose not return the 'real' content' per post；
  151
  152 _Posts = BlogService.FillPosts( );
  153 }
  154 return _Posts;
  155 }
  156 }
  157}
  158
  159in XmlBlogProvider
  160
  161/**//// <summary>
  162/// Retrieves a post based on the specified Id.
  163/// </summary>
  164public override Post SelectPost(Guid id)
  165{
  166 string fileName = _Folder + "posts\\" + id.ToString() + ".xml";
  167 Post post = new Post();
  168 XmlDocument doc = new XmlDocument();
  169 doc.Load(fileName);
  170
  171 post.Title = doc.SelectSingleNode("post/title").InnerText;
  172 post.Description = doc.SelectSingleNode("post/description").InnerText;
  173
  174 post.Content = null; // dose not return the 'real' content'
  175
  176 post.DateCreated = DateTime.Parse(doc.SelectSingleNode("post/pubDate").InnerText);
  177 post.DateModified = DateTime.Parse(doc.SelectSingleNode("post/lastModified").InnerText);
  178
  179 // setting other fileds
  180
  181 return post;
  182}

  个人觉得是否应该对于Content、Comment这种占用大量内存的字段是否该采用类似Lazy Initialization 的方式
  说明：第一次加载所有post时候 post list内的item不带真实的comtent和comment等
  然后在用到的时候再从数据库读取，然后放入缓存，下次备用
  这样Posts内的item都变的瘦多了，类似于延迟初始化（Lazy Initialization ）

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