问题
public class SearchText
{
public virtual int Id { get; set; }
public virtual string Text { get; set; }
}
public class SearchTextLog
{
public virtual int Id { get; set; }
public virtual SearchText SearchText { get; set; }
public virtual User User { get; set; }
public virtual int SearchCount { get; set; }
public virtual DateTime LastSearchDate { get; set; }
}
I am trying to select the top 5 SearchText items based on the sum of their count within the SearchTextLog. Currently I have only been able to resolve this by first performing a query to get the top 5 items, and then using the result within a second query. I was wondering if someone could show me the light and teach me how I could integrate these two seperate queries into a single unit.
Here is what I have currently:
var topSearchCriteria = Session.CreateCriteria(typeof (SearchTextLog))
.SetProjection(Projections.ProjectionList()
.Add(Projections.GroupProperty("SearchText.Id"))
.Add(Projections.Alias(Projections.Sum("SearchCount"), "SearchCount")))
.AddOrder(Order.Desc("SearchCount"))
.SetMaxResults(topSearchLimit)
.List<int>();
return Session.CreateCriteria<SearchText>()
.Add(Restrictions.In("Id", topSearchCriteria.ToArray()))
.List<SearchText>();
Edit:
Oh no, I just realised my current solution will lose the important order by of the results. So I will definitely have to incorporate the queries. :-/
Edit:
I tried a bidirectional mapping too to allow the following statement, however, I can't get it to return SearchText items. It simply complains that the SearchText properties aren't in a grouping.
return Session.CreateCriteria<SearchText>()
.CreateAlias("SearchTextLogs", "stl")
.AddOrder(Order.Desc(Projections.Sum("stl.SearchCount")))
.SetMaxResults(topSearchLimit)
.SetResultTransformer(Transformers.AliasToEntityMap)
.List<SearchText>();
Excuse my ignorance, but Nhibernate is completely new to me, and requires a completely different way of thinking.
回答1:
Ok, I think I have figured out a solution.
My original solution as per my question won't work because NHibernate doesn't yet support the ability to do a group by property without adding it to the select clause (see: link text).
While fooling around however, I came across these cool things called ResultTransformers. Using the AliasToBean result transformer Nhibernate will automatically map the alias's I give to each projection item to properties by the same name within a type I specify. I simply specified my SearchText object (however, I had to add an additional TotalSearchCount property for the sum projection item). It populated my objects perfectly and returned them.
return Session.CreateCriteria(typeof(SearchTextLog))
.CreateAlias("SearchText", "st")
.SetProjection(Projections.ProjectionList()
.Add(Projections.Alias(Projections.GroupProperty("st.Id"), "Id"))
.Add(Projections.Alias(Projections.GroupProperty("st.Text"), "Text"))
.Add(Projections.Alias(Projections.Sum("SearchCount"), "TotalSearchCount")))
.SetMaxResults(topSearchLimit)
.AddOrder(Order.Desc("TotalSearchCount"))
.SetResultTransformer(Transformers.AliasToBean(typeof(SearchText)))
.List<SearchText>();
I am surprised this wasn't easier to do. It's taken me about 4 to 5 hours of research and dev to figure this one out. Hopefully my NHibernate experience will get easier with more and more experience.
I hope this helps someone else out there!
回答2:
doesn't this work?
var critterRes = Session.CreateCriteria(typeof (SearchTextLog))
.SetProjection(Projections.ProjectionList()
.Add(Projections.GroupProperty("SearchText"))
.Add(Projections.Property("SearchText"))
.Add(Projections.Alias(Projections.Sum("SearchCount"), "SearchCount")))
.AddOrder(Order.Desc("SearchCount"))
.SetMaxResults(topSearchLimit)
.List<SearchText>()
来源:https://stackoverflow.com/questions/3290076/nhibernate-criteria-select-items-by-the-group-by-and-sum-of-itemid-within-anothe