NHibernate:返回已应用聚合函数的强类型列表 [英] NHibernate: returning a strongly typed list having applied an aggregate function

问题描述

我想让nHibernate从使用HQL的CreateQuery调用返回一个强类型列表.

I'd like to have nHibernate return a strongly typed list from a CreateQuery invocation using HQL.

我们希望返回一个强类型的"MyType"列表，但我们希望在返回结果集之前将聚合函数应用于结果集.不幸的是，据我了解，添加聚合字段意味着nHibernate无法将结果与我们的"MyType"类型的签名匹配.

We'd like a strongly typed list of "MyType" returned, but we'd like to apply an aggregate function to the resultset before it's returned. Unfortunately, as I understand it, adding the aggregate field means nHibernate is unable to match the results to the signature of our "MyType" type.

我们如何解决这个问题?以下查询描述了我们希望从数据库返回的内容-但是"feedcount"字段会影响nHibernate确定要返回的类型列表的能力.

How do we get around this? The following query describes what we'd like to return from the database - but the "feedcount" field affects nHibernate's ability to determine the typed list to return.

select feedname, count(feedurl) as feedcount from rsssubscriptions group by feedurl, feedname order by feedcount desc

大概必须在事件序列中更早地生成结果集，以确保nHibenate可以推断出正确的类型以为每个记录实例化.

Presumably the resultset has to be generated earlier in the sequence of events, to ensure nHibenate can infer the correct type to instantiate for each record.

谢谢

推荐答案

这是您需要做的:

IList<MyObj> reults = Session.CreateQuery("select r.feedname as feedname, count(r.feedurl) as feedcount from rsssubscriptions r group by r.feedname")
                            .SetResultTransformer(NHibernate.Transform.Transformers.AliasToBean(typeof(myobj)))
                            .List<MyObj>();

然后像这样定义MyObj类型:

And then define the MyObj type like this:

public class MyObj 
{
    public virtual long feedcount { get; set; }
    public virtual string feedname { get; set; }
}

上述类型的属性名称必须与返回的属性的别名相同，并且所有属性都必须是虚拟的.

The property names of the above type must be the same as the aliases of your returned properties and all properties must be virtual.

阅读以下文章，详细了解您可以使用SetResultTransformer()方法执行的操作: http://www.junasoftware.com/blog/nhibernate-setresulttransformer-和-dto.aspx

Read the following post on more info on what you can do with the SetResultTransformer() method: http://www.junasoftware.com/blog/nhibernate-setresulttransformer-and-dto.aspx

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