原文链接：http://www.cnblogs.com/debug1/archive/2006/05/19/413756.html

　　在上一篇处理继承关系中，我们介绍了使用Subclass和Discriminator来实现简单的继承关系。这一篇，将介绍如何使用Discriminator来实现稍微复杂一些的继承关系。

　　在此之前，要先说明一下：本次设计中的实体类都未继承自ActiveRecordBase。所以这里还要引入ActiveRecordMediator类，它可以让没有继承自ActiveRecordBase的实体使用ActiveRecord的功能。
ActiveRecordMediator
  Namespace: Castle.ActiveRecord
  Assembly:    Castle.ActiveRecord (in Castle.ActiveRecord.dll)

来看实体类设计：

[基类]

public abstract class EntityBase { private int _id; public EntityBase() { } /// /// 虽然类没有打上"ActiveRecord"属性标签， /// 但该属性在子类中将被做为主键持久化到数据库 /// [PrimaryKey(PrimaryKeyType.Native, "id")] public int ID { get { return _id; } set { _id = value; } } public virtual void Save() { ActiveRecordMediator.Save(this); } public virtual void Create() { ActiveRecordMediator.Create(this); } public virtual void Update() { ActiveRecordMediator.Update(this); } public virtual void Delete() { ActiveRecordMediator.Delete(this); } public virtual object Execute(NHibernateDelegate call) { return ActiveRecordMediator.Execute(this.GetType(), call, this); } }

请注意，实体类中ID属性被上打了"PrimaryKey"标签，另外EntityBase里还包含了基本的实例方法 Save()，Create()，Update()，Delete()，Execute()。

[论坛类]

[ActiveRecord("Forum")] public class ForumEntity : EntityBase { private string _name; private IList _posts = new ArrayList(); public ForumEntity() { } public ForumEntity(string name) { this._name = name; } [Property("name")] public string Name { get { return _name; } set { _name = value; } } [HasMany(typeof(Posts), Table = "Thread", ColumnKey = "forum_id", Cascade = ManyRelationCascadeEnum.All)] public IList Posts { get { return _posts; } set { _posts = value; } } public static void DeleteAll() { ActiveRecordMediator<ForumEntity>.DeleteAll(); } public static ForumEntity[] FindAll() { return ActiveRecordMediator<ForumEntity>.FindAll(); } public static ForumEntity Find(int id) { return ActiveRecordMediator<ForumEntity>.Find(id); } public static ForumEntity TryFind(int id) { return ActiveRecordMediator<ForumEntity>.TryFind(id); } }

由于在EntityBase中已经指定了PrimaryKey，所以ForumEntity类中没有再给他指定主键字段（下面的ThreadEntity类也是如此）。

[主题跟回帖类]

[ActiveRecord(DiscriminatorValue = "post")] public class Posts : ThreadEntity { private ForumEntity _forum; public Posts() { } public Posts(string author, string title) : base(author, title) { } [BelongsTo("forum_id")] public ForumEntity Forum { get { return _forum; } set { _forum = value; } } public static void DeleteAll() { ActiveRecordMediator<Posts>.DeleteAll(); } public static Posts[] FindAll() { return ActiveRecordMediator<Posts>.FindAll(); } public static Posts Find(int id) { return ActiveRecordMediator<Posts>.Find(id); } public static Posts TryFind(int id) { return ActiveRecordMediator<Posts>.TryFind(id); } } [ActiveRecord(DiscriminatorValue = "reply")] public class Replies : ThreadEntity { private Posts _post; public Replies() { } public Replies(string author, string title) : base(author, title) { } [BelongsTo("post_id", Insert = false, Update = false, Cascade = CascadeEnum.None)] public Posts Post { get { return _post; } set { _post = value; } } public static void DeleteAll() { ActiveRecordMediator<Replies>.DeleteAll(); } public static Replies[] FindAll() { return ActiveRecordMediator<Replies>.FindAll(); } public static Replies Find(int id) { return ActiveRecordMediator<Replies>.Find(id); } public static Replies TryFind(int id) { return ActiveRecordMediator<Replies>.TryFind(id); } }

这里的Thread可以理解为主题(Post)和回帖(Reply)的集合。

可以运行下面的代码做个简单测试：

private void Test() { ForumEntity forum = new ForumEntity("Castle ActiveRecord"); forum.Create(); ForumEntity f1 = ForumEntity.TryFind(1); MessageBox.Show(f1 == null ? "forum not found..." : "Forum:" + f1.Name); if (f1 != null) { Posts post = new Posts("debug_fan", "post-1"); post.Forum = f1; post.Create(); Posts p1 = Posts.TryFind(1); MessageBox.Show(p1 == null ? "post not found..." : "Post:\"" + p1.Title + "\" belongs to [Forum:" + (p1.Forum == null ? "" : p1.Forum.Name) + "]"); if (p1 != null) { Replies reply = new Replies("fan", "re: " + p1.Title); reply.Post = p1; reply.Create(); Replies r1 = Replies.FindAll()[0]; MessageBox.Show(r1 == null ? "reply not found..." : "Reply:\"" + r1.Title + "\" belongs to [Post:" + (r1.Post == null ? "" : r1.Post.Title) + "]"); } } }

 

文章来源:http://www.agilelabs.cn/blogs/%e8%8c%83%e4%bf%8a/archive/2006/05/19/1227.aspx

转载于:https://www.cnblogs.com/debug1/archive/2006/05/19/413756.html