NHibernate:如何在投影中选择根实体 [英] NHibernate: How to select the root entity in a projection

问题描述

Ayende在这里描述了一种获取页数的绝佳方法，并在单个查询中提供了特定数据页:

Ayende describes a really great way to get page count, and a specific page of data in a single query here:

http://ayende. com/blog/2334/paged-data-count-with-nhibernate-really-easy-way

他的方法如下:

IList list = session.CreateQuery("select b, rowcount() from Blog b")
              .SetFirstResult(5)
              .SetMaxResults(10)
              .List();

唯一的问题是此示例在HQL中，并且我需要在ICriteria查询中执行相同的操作.为了达到与ICriteria相同的效果，我需要做类似的事情:

The only problem is this example is in HQL, and I need to do the same thing in an ICriteria query. To achieve the equivalent with ICriteria, I need to do something like:

IList list = session.CreateCriteria<Blog>()
              .SetFirstResult(5)
              .SetMaxResults(10)
              .SetProjection(Projections.RootEntity(), Projections.SqlFunction("rowcount", NHibernateUtil.Int64))
              .List();

问题在于没有Projections.RootEntity()之类的东西.有什么方法可以选择根实体作为投影列表中的投影之一?

The problem is there is no such thing as Projections.RootEntity(). Is there any way to select the root entity as one of the projections in a projection list?

是的，我知道我可以只使用CriteriaTransform.TransformToRowCount()，但这将需要执行两次查询-一次用于结果，一次用于行数.使用Futures可以减少一次往返，但可能会有所帮助，但是它仍然在SQL Server上执行两次查询.对于密集查询，这是不可接受的.我想避免开销，并在同一查询中返回行数和结果.

Yes, I know I could just use CriteriaTransform.TransformToRowCount() but that would require executing the query twice - once for the results and once for the row count. Using Futures may help a little by reducing it to one round-trip, but it's still executing the query twice on the SQL Server. For intensive queries this is unacceptable. I want to avoid the overhead, and return the row count and the results in the same query.

基本问题是:使用ICriteria，是否可以同时选择根实体和其他一些投影?

The basic question is: using ICriteria, is there any way to select the root entity AND some other projection at the same time?

一些相关链接:

https://nhibernate .jira.com/browse/NH-1372?jql = text％20〜％20％22entity％20projection％22

https://nhibernate.jira.com/browse/NH-928

推荐答案

我实现了RootEntityProjection.您可以尝试在以下位置找到该代码:

I implemented a RootEntityProjection. You can try the code, which you can find at: http://weblogs.asp.net/ricardoperes/archive/2014/03/06/custom-nhibernate-criteria-projections.aspx. Let me know if it helped.

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