用Fluent nHibernate映射到多个表 [英] Mapping to multiple tables with Fluent nHibernate

问题描述

这是我的情况。

假设你有以下模型实体，它们自己代表单个表格：$ b $bâ€
电影 [Movie_Id，Title，Rating，..]

Actors [Actor_Id，FirstName，LastName，..]

导演 [Director_Id，FirstName，LastName，..]



另一个名为Recommendations的实体/表格表示用户一个网站。这个想法是推荐可以是任何类型的，即有人推荐一个演员，或某人推荐一部电影。基本上，这个表应该是这样的：
...
建议 [Recommendation_Id，Object_Id，Object_Type，..]



这里是我陷入了困境。如何将这些关系映射到nHibernate中与Fluent？
我的意思是，在映射时，我不能指定类型（与哪个表相关），因为这是在运行时确定的，但是我不能仅仅依靠Id本身，因为它不能暗示哪个
例如，想象一下在Recommendations表上的记录：

Recommendation_Id - Object_Id - Object_Type
b $ b 83001 --4010123 ---M

基本上我存储一个字符标识符（在这种情况下，M代表表电影），以知道Object_Id属于哪个表至。作为最终的评论，我想补充一点，我已经看到了所有的每班表格，table-per-subclass，table-per-concrete-class的例子，但是我相信这些都不适合这种情况，因为Movies_Id，Actors_Id，Directors_Id，...都是不同的，Recommendations_Id也是如此。我的意思是，在这里没有基类的子类继承，他们根本不共享Id。

我希望我自己清楚。
在此先感谢。

解决方案

您正在寻找的NHibernate映射是< any /> 。这里有一些资源可以帮助你加快这个NHibernate映射功能：

• Ayende的博文 NHibernate文档 com / jagregory / fluent-nhibernate / wiki / Fluent-mapping＃anyrel =noreferrer>流利的NHibernate文档 b
  

   < class name =推荐表格=建议> 
  < id name =Id> 
  < column name =Recommendation_Id/> 
  < generator class =native/> 
  < / id> 
   
  < any name =RecommendedObjectid-type =System.Int32meta-type =System.String> 
  < meta-value value =Mclass =Movie/> 
  < meta-value value =Aclass =Actor/> 
  < meta-value value =Dclass =Director/> 
  < column name =Object_Type/> 
  < column name =Object_Id/> 
  < / any> 
   
   <！ - 其他东西...  - > 
  < / class> 
    

  你应该可以用Fluent NHibernate来完成这个工作，就像在推荐的映射中一样：

    ReferencesAny（x => x.RecommendedObject）
   .IdentityType< int>（）
   .EntityTypeColumn（Object_Type ）
   .EntityIdentifierColumn（Object_Id）
   .AddMetaValue< Movie>（M）
   .AddMetaValue< Actor>（A）
   .AddMetaValue< Director>（ d）; 
    

  
  

  Here's my situation..
  Suppose you have the following model entities, which represent single tables on their own:
  
  Movies [ Movie_Id, Title, Rating, .. ]
  Actors [ Actor_Id, FirstName, LastName, .. ]
  Director [ Director_Id, FirstName, LastName, .. ]
  
  And another entity/table called "Recommendations", which represents recommendations between users within a website. The idea is that a recommendation could be of any type, i.e. someone recommending an actor, or someone recommending a movie. Basically, the table should look something like this:
  
  Recommendations [ Recommendation_Id, Object_Id, Object_Type, .. ]
  
  And here's what i'm stuck into. How can I map these relationships in nHibernate with Fluent? I mean.. while mapping, I can't specify the Type (which table related to) 'cause that's determined on runtime, but I can't rely only on the Id 'cause by itself it cannot imply to which table belongs to.
  For instance, imagine this record on Recommendations table:
  
  Recommendation_Id--Object_Id--Object_Type
  83001--4010123---"M"
  
  Basically I'm storing a char identifier (in this case "M" stands for table "Movies") to know to which table Object_Id belongs to. I cannot just store Object_Id without Object_Type..
  

  As final comments, I'd like to add that I've seen all the table-per-class, table-per-subclass, table-per-concrete-class examples, but I believe none of these fits in this situation, as Movies_Id, Actors_Id, Directors_Id, ... are all different between them, so is Recommendations_Id. I mean, there's no base class-child class inheritance here, they don't share Id's at all..

  I hope I make myself clear. Thanks in advance.

  解决方案

  The NHibernate mapping you are looking for is <any/>. Here are a few resources to help you get up to speed with this NHibernate mapping feature:

  • Ayende's blog post
  • NHibernate documentation
  • Fluent NHibernate documentation

  I believe the *.hbm.xml that you are shooting for is something like this:

  <class name="Recommendation" table="Recommendations">
    <id name="Id">
      <column name="Recommendation_Id" />
      <generator class="native"/>
    </id>
  
    <any name="RecommendedObject" id-type="System.Int32" meta-type="System.String">
      <meta-value value="M" class="Movie"/>
      <meta-value value="A" class="Actor"/>
      <meta-value value="D" class="Director"/>
      <column name="Object_Type"/>
      <column name="Object_Id"/>
    </any>
  
    <!-- other stuff ... -->
  </class>
  

  You should be able to accomplish that with Fluent NHibernate like so in Recommendation's mapping:

  ReferencesAny(x => x.RecommendedObject)
      .IdentityType<int>()
      .EntityTypeColumn("Object_Type")
      .EntityIdentifierColumn("Object_Id")
      .AddMetaValue<Movie>("M")
      .AddMetaValue<Actor>("A")
      .AddMetaValue<Director>("D");
  

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