How to convert SQL aggregate query into NHibernate Criteria Query

I'm new to 开发者_StackOverflow中文版Criteria API in NHibernate. Can someone generate this piece of SQL using Criteria API in NHibernate?

select count(*) 
from result where Student_id 
in(
  SELECT s.Student_id 
  from Department as d
  JOIN Student s ON d.Dept_id=s.Dept_id
  where d.Dept_id=2
)

and how to proceed through the Criteria API in NHibernate. P.S I don't want to use HQL so without HQL is it possible to generate this kind of sql in nhibernate?

You can use linq-2-nhibernate as well.

Given the following class structure:

public class Result{
    public virtual Student Student {get; set;}
}

public class Student{
    public virtual Department Department {get; set;}
    public virtual int Id { get; set;}
}

public virtual Department {
    public virtual int Id {get; set;}
    public virtual IList<Student> Students {get; set;}
} 

Here is your query using the Criteria API:

var studentidquery = DetachedCriteria.For<Student>()
  .Add(Restrictions.Eq("Department.Id"),2)
  .SetProjection(Projections.Property("Id"));

var count = session.CreateCriteria<Result>()
   .Add(Subqueries.PropertyIn("StudentId", studentidquery))
   .UniqueResult<int>();

Using the QueryOver API it would look like this:

var studentidquery = QueryOver.Of<Student>()
  .Where(x=>x.Department.Id==2)
  .Select(x=>x.Id);

var count = session.QueryOver<Result>()
   .WithSubquery.WhereProperty(x => x.Id).In(studentidquery)
   .Select(Projections.Count<Result>(r=>r.Id))
   .UniqueResult<int>();

Also I don't think you need the join to Department in your SQL query as you already have DepartmentId as a foreign key in the Student table. No sense in joining to extra tables for no good reason.