Castle ActiveRecord(三) 关联映射
ActiveRecord 提供一个DomainModel 工具,它使我们创建对象模型的相互关系非常容易。在上面的例子中我们已经创建了一个Blog类,它完全可以提供一个Post类及它们之间的关联。平白点讲,他们的关联是:
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一个Post属于一个Blog
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一个Blog有多个Post
使用HasMany特性 和BelongsTo特性
必须使用HasMany和BelongTo特性表达对象之间的关联。如下:
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在这个例子中,由于Post有一个BelongTo联合,ActiveRecord能够收集到这个信息并创建正确的HasMany,因此不必指定所有信息,象下面这样就可以了,注意对比“[HasMany(typeof(Post))]”:
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不要感到疑惑,让我们看看Post类,注意[BelongsTo("post_blogid")]:
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好,我们来看看怎么使用关联映射吧。先看下面的代码:
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这段代码是无法正常运行的,因为Post类是一个瞬态类,在使用时我们必须先持久化它,象下面这样就可以运行了:
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不过你的Blogs表中要有记录才行,否则会发生异常,告诉你找不到。又有人不禁想出了下面的代码:
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这样还是不行地,在向数据库里面保存时,Post实际需要的是Blog的Id,而此时Blog还没有Id。
上面的代码都使用了Blog端的关联,也可以象下面这样使用:
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处理blog的时候,Posts不会自动地得到通知。如果想应用最新的改变,也好就是说要想使用新实例化的post,必须“刷新”它。我们可以通过设置级联变化来使用它:
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这样的开头那段代码就能运行了:
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怎么样,一定有点晕了吧,不要紧,下一节我们将讲解一下HasManyAttribute和BelongsToAttribute。