NHibernate - 获取具有分页子集合的父级

Question

我目前正在编写一个非常基本的在线论坛，我想检索带有分页帖子子集合的线程。所以我的映射是：

<class name="Thread" table="ForumThreads">
    <id name="Id">
        <generator class="identity"></generator>
    </id>

    <property name="Title"></property>

    <bag name="Posts">
        <key column="ThreadID"></key>
        <one-to-many class="Post"/>
    </bag>
</class>

<class name="Post" table="ForumPosts">
    <id name="Id">
        <generator class="identity"></generator>
    </id>

    <property name="Content"></property>

    <many-to-one name="Thread"
                 class="Thread"
                 column="ThreadID">
    </many-to-one>
</class>

我想做这样的事情：

public class Thread
{
    public virtual int Id { get; set; }
    public virtual string Title { get; set; }
    public virtual IEnumerable<Post> Posts { get; set; }
}

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

public Thread GetThread(int threadId, int page, int pageSize, out int count)
{
    var session = SessionFactory.CurrentSession;

    // Query to get the thread with a child collection of paged posts. 

    return thread;
}

是否可以通过一个查询来完成此操作，还是必须将其分成两个？

谢谢

Answer 1

var threadId = ...
session.QueryOver<Thread>
  .Where(thread => thread.Id == threadId)
  .Fetch(thread => thread.Posts).Eager
  .Take(pageSize)
  .Skip(page)
  .TransformUsing(Transformers.DistinctRootEntity)
  .List<Thread>();

Answer 2

如果您正在考虑进行数据库级分页，那么方法将是这样的，

1. 你必须使用集合来支持额外模式的延迟加载

2. 您可能需要使用过滤器来加载集合，（但您不能返回线程作为结果，就好像您尝试访问集合它将加载所有帖子一样）

   public List<Post> GetThreadPosts(int threadId, int page, int pageSize, out int count)
   {
       var session = SessionFactory.CurrentSession;
        Thread thread = (Thread )session.Get(typeof(Thread ), threadId);
        var posts = session.CreateFilter(thread .Posts, "").SetFirstResult((page - 1)  * pageSize).SetMaxResults(pageSize).List();
   
       return posts ;
   }