NHibernate的QueryOver繼承

Question

我有這樣的事情：

public class User 
    { 
     /* some properties */ 
     public virtual int Id { get; set; } 
     public abstract string LastName { get; } 

    } 
    public class Student 
    { 
     public virtual int Id { get; set; } 
     public virtual string LastName{ get; set; } 
    } 

    public class StudentUser : User 
    { 
     public virtual Student Student { set; get; } 

     public override string LastName 
     { 
      get { return Student.LastName; } 
     } 
    } 

    public class foo 
    { 
     public virtual int Id { get; set; } 

     public virtual IList<User> Users { get; set; } 
    } 


1. I would like to do the following using QueryOver : 
    var query = session.QueryOver<foo>(); 
     User User = null; 

//case 1: This is not working 
     query.JoinAlias(x=> x.Users ,() => User) 
       .Where(() => ((StudentUser)User).Student.LastName == "smith"); 

//case 2: Also This is not working 
     query.JoinAlias(x=> x.Users ,() => User) 
       .Where(() => ((StudentUser)User).LastName == "smith"); 

//case 3: This is working 
     query.JoinAlias(x=> x.Users ,() => User) 
       .Where(() => ((StudentUser)User).Id == 123); 

當我使用query.JoinAlias(x=> x.Users ,() => User)超過一次，我得到這個例外An item with the same key has already been added。

而且我得到這個異常：無法解析屬性：的Student.LastName：Entities.User的情況下，1和2的情況下

但它正在與Id屬性（案例3）

它可能看起來像：

SELECT  * 
FROM   Foo INNER JOIN 
         Users ON Foo.Id = Users.FooId_FK INNER JOIN 
         Students ON Users.StudentId_FK = Students.Id 
where Students.LastName = 'smith' 

我怎樣才能得到LastName屬性值？

Answer 1

我認爲這應該工作：

session.QueryOver<foo>() 
    .JoinQueryOver(f => f.Users) 
    .JoinQueryOver(u => ((StudentUser)u).Student) 
     .Where(st => st.LastName == "smith") 

或用JoinAlias保持：

User userAlias = null; 
Student studentAlias = null; 

session.QueryOver<foo>() 
    .JoinAlias(f => f.Users,() => userAlias) 
    .JoinAlias(() => ((StudentUser)userAlias).Student,() => studentAlias) 
     .Where(() => studentAlias.LastName == "smith")