NHibernate的許多-to-one和雙向訪問

Question

什麼HBM我必須寫Blog和Post有這些表之間的雙向關係？

我試圖從兩邊many-to-one但碰到以下問題（很可能是因爲我做到了完全錯誤的）：

• 瞬態持久性錯誤，在一個Session插入對象圖。
• 與Blog和Post表引用彼此外交的關鍵問題。

注意：我的例子是人爲設計的，請不要爭論設計。

設計：

來源：

public class Blog 
{ 
    public virtual int Id { get; set; } 
    public virtual string Name { get; set; } 
    public virtual Comment LastComment { get; set; } // last-comment 

    public virtual IList<Post> Posts { get; set; } 
} 

public class Post 
{ 
    public virtual int Id { get; set; } 
    public virtual string Content { get; set; } 

    public virtual IList<Comment> Comments { get; set; } 
} 

public class Comment 
{ 
    public virtual int Id { get; set; } 
    public virtual string Feedback { get; set; } 
    public virtual Blog Blog { get; set; } //commented-on 
} 

HBM：

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Sample" 
namespace="Sample"> 
    <class name="Blog"> 
    <id name="Id"> 
     <generator class="hilo" /> 
    </id> 
    <property name="Name" /> 
    <!-- How to map Comment? --> 
    <bag name="Posts"> 
     <key column="BlogId" /> 
     <one-to-many class="Post" /> 
    </bag> 
    </class> 

    <class name="Post"> 
    <id name="Id"> 
     <generator class="hilo" /> 
    </id> 
    <property name="Feedback" /> 
    <bag name="Comments"> 
     <key column="PostId" /> 
     <one-to-many class="Comment" /> 
    </bag> 
    </class> 

    <class name="Comment"> 
    <id name="Id"> 
     <generator class="hilo" /> 
    </id> 
    <property name="Comment" /> 
    <!-- How to map back to Blog? --> 
    </class> 
</hibernate-mapping> 

所需DB結構：

+------------------------------+ 
| Blog       | 
+--------------+---------------+ 
| Id   | int   | 
| Name   | nvarchar(50) | 
| LastCommentId| int (null) | 
+--------------+---------------+ 

+------------------------------+ 
| Post       | 
+--------------+---------------+ 
| Id   | int   | 
| BlogId  | int   | 
+--------------+---------------+ 

+------------------------------+ 
| Comment      | 
+--------------+---------------+ 
| Id   | int   | 
| PostId  | int   | 
| BlogId  | int (not-null)| 
| Feedback  | nvarchar(200) | 
+--------------+---------------+ 

Answer 1

你需要一個博客屬性添加到後如果它需要非空（見在6.4. One-To-Many Associations最後一段）

這裏有一些映射，應該工作：

<class name="Blog" dynamic-update="true"> 
    <id name="Id"> 
    <generator class="..."/> 
    </id> 
    <property name="Name" /> 
    <many-to-one name="LastComment" column="LastCommentId" cascade="all" /> 
    <bag name="Posts" cascade="all" inverse="true"> 
    <key column="BlogId" /> 
    <one-to-many class="Post" /> 
    </bag> 
</class> 
<class name="Post"> 
    <id name="Id"> 
    <generator class="..."/> 
    </id> 
    <property name="Content" /> 
    <many-to-one name="Blog" column="BlogId" /> 
    <bag name="Comments" inverse="true"> 
    <key column="PostId" /> 
    <one-to-many class="Comment" /> 
    </bag> 
</class> 
<class name="Comment"> 
    <id name="Id"> 
    <generator class="..."/> 
    </id> 
    <property name="Feedback" /> 
    <many-to-one name="Blog" column="BlogId" not-null="true" cascade="all" /> 
</class> 

然後你就可以使用如下代碼：

using (var session = sessionFactory.OpenSession()) 
using (var tx = session.BeginTransaction()) 
{ 
    var blog = new Blog { Name = "My Blog" }; 
    var post = new Post { Blog = blog, Content = "My First Post" }; 
    var comment = new Comment { Blog = blog, Feedback = "Awesome!" }; 
    blog.LastComment = comment; 
    blog.Posts = new List<Post> { post }; 
    post.Comments = new List<Comment> { comment }; 
    session.Save(comment); 
    tx.Commit(); 
} 

這就將博客，則郵政，則在評論，則更新博客設置LastCommentId。

請注意，您需要致電保存對評論;別的什麼都會失敗。