[C#][Videgree] 為了封裝"附加(Attachment)"功能，使用了 "Interface + Method Extension + 繼承" 硬是把它給生出來

2012-03-20

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C#

前言 : 這是我在公司寫"Videgree愛顧客"這產品時，所遇到的一個很有趣的情境，為了降低重複的程式碼，很用力的寫出這個方式出來

故事的開始 : 有一天老大跟大家討論，如果我們產品"記事(Note)"這功能，能夠有類似FB塗鴉牆的功能的話，那麼User在使用上就能更方便的張貼

自己想要的內容，而不是單純的只有文字描述，所以希望Note能夠有掛上"附件(Attachment)"的能力(就像FB，G+的訊息功能一樣)，

可以上傳一個檔案，連結一張圖或是連一個blog網站之類的，於是乎就有這樣的Domain Model

簡單的解釋這張圖 : 首先主角Note，附件Attachment跟它的兒子們(SubType)，每個note都可以掛上上多種Attachment

物件的關係看起來非常之簡單但因應它的變化就要很小心

先看Attachment的interface 跟Impl，UploadedFile這顆物件存放是實體檔案的相關資訊，上方我沒有畫出來，也就只有File 跟MailEmbeddedImg會用到

   1:      public interface IAttachment : IEntity

   2:      {

   3:          string Description { get; set; }

   4:          INote Note { get; set; }

   5:      }

6:

   7:      public interface IFileAttachment : IAttachment

   8:      {

   9:          string FileName { get; set; }

  10:          IUploadedFile UploadedFile { get; set; }

  11:      }

12:

  13:      public interface ILinkAttachment : IAttachment

  14:      {

  15:          Uri AttachmentUrl { get; set; }

  16:      }

17:

  18:      public interface IMailEmbeddedImg : IAttachment

  19:      {

  20:          string FileName { get; set; }

  21:          IUploadedFile UploadedFile { get; set; }

  22:      }

23:

  24:      // 實作部份

  25:      public class Attachment : Entity, IAttachment

  26:      {

  27:          public virtual string Description { get; set; }

  28:          public virtual INote Note { get; set; }

  29:      }

30:

  31:      public class FileAttachment : Attachment, IFileAttachment

  32:      {

  33:          public virtual string FileName { get; set; }

  34:          public virtual IUploadedFile UploadedFile { get; set; }

  35:      }

36:

  37:      public class LinkAttachment : Attachment, ILinkAttachment

  38:      {

  39:          public virtual Uri AttachmentUrl { get; set; }

  40:      }

41:

  42:      public class MailEmbeddedImg : Attachment, IMailEmbeddedImg

  43:      {

  44:          public virtual string FileName { get; set; }

  45:          public virtual IUploadedFile UploadedFile { get; set; }

  46:      }

接下來看Note的Interface跟實作

   1:      public interface INote : IEntity, IAttachable

   2:      {

   3:          //咦?Note只有這個屬性，要注意繼承後面又跟了一個IAttachable，我們把Attachment相關的動作定到這個Interface上了

   4:          string Description { get; set; }

   5:      }

6:

   7:      public class Note : Entity, INote

   8:      {

   9:          public virtual string Description { get; set; }

10:

  11:          /* 以下的部份全部都在實作IAttachable所訂出來的Method跟屬性 */

  12:          //附加檔案的集合

  13:          private IList attachments = new ArrayList();

  14:          public virtual IList Attachments

  15:          {

  16:              get { return attachments; }

  17:              set { attachments = value; }

  18:          }

19:

  20:          //處理增加一個Link的Attachment

  21:          public virtual ILinkAttachment AddAttachments(ILinkAttachment linkAttachment)

  22:          {

  23:              linkAttachment.Note = this;

  24:              this.Attachments.Add(linkAttachment);

  25:              return linkAttachment;

  26:          }

  27:          //處理增加一個File的Attachment

  28:          public virtual IFileAttachment AddAttachments(IFileAttachment fileAttachment)

  29:          {

  30:              fileAttachment.Note = this;

  31:              this.Attachments.Add(fileAttachment);

  32:              return fileAttachment;

  33:          }

  34:          //處理增加一個Mail Embedded的圖檔

  35:          public virtual IMailEmbeddedImg AddAttachments(IMailEmbeddedImg mailEmbeddedImg)

  36:          {

  37:              mailEmbeddedImg.Note = this;

  38:              this.Attachments.Add(mailEmbeddedImg);

  39:              return mailEmbeddedImg;

  40:          }

  41:      }

42:

  43:      /* 最後再來看看IAttachable這個Interface，它定了物件存放Attachment集合的屬性，

  44:            並且把各種Attachment類型的新增方式也定下來*/

  45:      public interface IAttachable

  46:      {

  47:          IList Attachments { get; set; }

48:

  49:          ILinkAttachment AddAttachments(ILinkAttachment linkAttachment);

50:

  51:          IFileAttachment AddAttachments(IFileAttachment fileAttachment);

52:

  53:          IMailEmbeddedImg AddAttachments(IMailEmbeddedImg mailEmbeddedImg);

  54:      }

看到這邊應該就會有幾個問題了，

1.為什麼要另外定一個IAttachable?

2.那三個Add Attachment的Method只做物件關聯，其他啥事都沒做，而且名稱都一樣?

其實會定IAttachable是為了，把Attachment給獨立出來，之後只要有其他物件(如: 公告Announcement，工作Task)有需要掛上附件的話，

只要實作這個 Interface –> IAttachable，那麼這物件自然就有能力可以掛上Attachment

而在Note的實作上那三個Add Attachment的Method只做物件關聯，是因為只有物件關聯的部份無法獨立出來，

其他的邏輯部份不管你現在是使用那個物件(Note，Announcement，Task)，其實邏輯都一樣，所以我們把它寫到Attachable Extension如下:

   1:      public static class AttachableExtension

   2:      {

   3:          public static ILinkAttachment AddLinkAttachment(this IAttachable attachable, string description, Uri url)

   4:          {

   5:              ILinkAttachment linkAttachment = RheaFactory.DomainFactory.MakePreProcessDomain<ILinkAttachment>();

   6:              linkAttachment.Description = description;

   7:              linkAttachment.AttachmentUrl = url;

   8:              attachable.AddAttachments(linkAttachment);

   9:              return linkAttachment;

  10:          }

11:

  12:          public static IFileAttachment AddFileAttachment(this IAttachable attachable, string description, string fileName, string eigenvalue, long fileSize)

  13:          {

  14:              IFileAttachment fileAttachment = RheaFactory.DomainFactory.MakePreProcessDomain<IFileAttachment>();

  15:              fileAttachment.Description = description;

  16:              fileAttachment.FileName = fileName;

  17:              attachable.AddAttachments(fileAttachment);

  18:              return fileAttachment;

  19:          }

20:

  21:          public static IMailEmbeddedImg AddMailEmbeddedImg(this IAttachable attachable, string description, string fileName, string eigenvalue, long fileSize)

  22:          {

  23:              IMailEmbeddedImg mailEmbeddedImg = RheaFactory.DomainFactory.MakePreProcessDomain<IMailEmbeddedImg>();

  24:              mailEmbeddedImg.Description = description;

  25:              mailEmbeddedImg.FileName = fileName;

  26:              attachable.AddAttachments(mailEmbeddedImg);

  27:              return mailEmbeddedImg;

  28:          }

  29:      }

在Extension部份可以看到粗體的attachable，這是定IAttachable 最主要的原因，

在外不用認識你是誰(Note，Announcement，Task)，我只要知道你有實做IAttachable ，

所以我就都用IAttachable 跟你溝通，在來我把Method名稱都定成一樣，就不用去知道

傳入的是種類型，會知道Attachment類型的當然是最外層的人，而這個Extension就是

給外層使用，所以只在這裡去命名外面人看的懂有意義類型的Method名稱

整個底都用好後使用起來就像這樣

   1:          [HttpPost]

   2:          [ValidateInput(false)]

   3:          public ActionResult Save(FormCollection collection)

   4:          {

   5:              INote note = RheaFactory.DomainFactory.MakeDomain<INote>();

   6:              // 加一個Add FileAttachment

   7:              note.AddFileAttachment(collection["Description"], collection["FileName"], collection["Eigenvalue"], 1024);

   8:              // 加一個Add LinkAttachment

   9:              note.AddLinkAttachment(collection["LinkDescription"], new Uri(collection["Url"]));

  10:              // 加一個Add MailEmbeddedImg

  11:              note.AddMailEmbeddedImg(collection["ImgDescription"], collection["ImgFileName"], collection["ImgEigenvalue"], 1024);

12:

  13:              NoteService.Create(note);

  14:          }

然後過沒兩天老大真的就說Announcement，Task等也都掛上可加Attachment的行為吧

所以我只需要做稍為的調整就行了~如下:

Attachment加上Announcement，Task

   1:      [Serializable]

   2:      public class Attachment : Entity, IAttachment

   3:      {

   4:          public virtual string Description { get; set; }

   5:          public virtual INote Note { get; set; }

   6:          public virtual IAnnouncement Announcement { get; set; }

   7:          public virtual ICase Case { get; set; }

   8:      }

Announcement的Interface掛上IAttachable

   1:      public interface IAnnouncement : IEntity, IAttachable

   2:      {

   3:          /// <summary>

   4:          /// 公告有效日期-起日(以日為單位)

   5:          /// </summary>

   6:          DateTime FromDate { get; set; }

7:

   8:          /// <summary>

   9:          /// 公告有效日期-迄日(以日為單位)

  10:          /// </summary>

  11:          DateTime ThruDate { get; set; }

12:

  13:          /// <summary>

  14:          /// 公告標題

  15:          /// </summary>

  16:          string Title { get; set; }

17:

  18:          /// <summary>

  19:          /// 公告內容

  20:          /// </summary>

  21:          string Content { get; set; }

22:

  23:          /// <summary>

  24:          /// 重要性

  25:          /// </summary>

  26:          EnumImportance Importance { get; set; }

  27:      }

Announcement補上IAttachable的實作

   1:      public class Announcement : Entity, IAnnouncement

   2:      {

   3:          public virtual DateTime FromDate { get; set; }

   4:          public virtual DateTime ThruDate { get; set; }

   5:          public virtual string Title { get; set; }

   6:          public virtual string Content { get; set; }

   7:          public virtual EnumImportance Importance { get; set; }

8:

   9:          private IList attachments = new ArrayList();

  10:          public virtual IList Attachments

  11:          {

  12:              get { return attachments; }

  13:              set { attachments = value; }

  14:          }

15:

  16:          public virtual ILinkAttachment AddAttachments(ILinkAttachment linkAttachment)

  17:          {

  18:              linkAttachment.Announcement = this;

  19:              this.Attachments.Add(linkAttachment);

  20:              return linkAttachment;

  21:          }

22:

  23:          public virtual IFileAttachment AddAttachments(IFileAttachment fileAttachment)

  24:          {

  25:              fileAttachment.Announcement = this;

  26:              this.Attachments.Add(fileAttachment);

  27:              return fileAttachment;

  28:          }

29:

  30:          public virtual IMailEmbeddedImg AddAttachments(IMailEmbeddedImg mailEmbeddedImg)

  31:          {

  32:              mailEmbeddedImg.Announcement = this;

  33:              this.Attachments.Add(mailEmbeddedImg);

  34:              return mailEmbeddedImg;

  35:          }

  36:      }

完成這幾個步驟後Announcement也就有掛上Attachment的能力了，Task也只要補上這幾個動作也就可以掛附件了

而上方提到的只有物件關聯的部份無法獨立出來，原因就是紅色字段的部份，在最後的部份還是要給個明確的物件當關聯

由於這是範例所以我拿掉很多code，像檔案的處理部份之類的，所以看的時候需要點想像力，辛苦了。

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