NHibernate Relationships in Oracle - nhibernate

Question

After countless hours of trying to make Entity Framework work with Oracle, I have given up and started down the path of NHibernate.
I am struggling with the lingo a bit, and have a question. Given the following classes, how do I make NHibernate (Fluent Mappings) output something similar to the SQL below using the WriteOffApprovalUser.UserName as the key to the Employee.MailID field.
C# Classes
public class WriteOffApprovalUser : EntityBase<WriteOffApprovalUser>
{
public virtual string UserName { get; set; }
public virtual Employee.Employee Employee { get; set; }
}
public class Employee : EntityBase<Employee>
{
public virtual string EmployeeID { get; set; }
public virtual string EmployeeStatusCode { get; set; }
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
public virtual string PreferredName { get; set; }
public virtual string JobTitle { get; set; }
public virtual string Division { get; set; }
public virtual string Department { get; set; }
public virtual string Location { get; set; }
public virtual string City { get; set; }
public virtual string DeskLocation { get; set; }
public virtual string MailID { get; set; }
public virtual string Phone { get; set; }
public virtual string Fax { get; set; }
public virtual string SecCode { get; set; }
public virtual string SupervisorID { get; set; }
}
SQL
SELECT c.user_name,
a.LAST_NAME
|| ', '
|| DECODE (a.PREFERRED_NAME, ' ', a.FIRST_NAME, a.preferred_name)
writeoff_approval_name
FROM writeoff_approval_user c, adp_employee a
WHERE c.USER_NAME = a.USER_ID AND c.exp_date IS NULL
ORDER BY 2

Answer 1

In NHibernate all is about mapping the right way. If you're using fluent you should have defined a reference in WriteOffApprovalUser to an Employee entity. Like in this basic tutorial
public class WriteOffApprovalUserMap : ClassMap<WriteOffApprovalUser>
{
public WriteOffApprovalUserMap()
{
Id(x => x.UserName);
References(x => x.Employee);
}
}
Then all you need to do is a simple query like
List<Employee> employees = session.Where(e => e.exp_date == null);
I haven't seen mapped any Date but I this easy to fix.
Then to have the DECODE feature I will suggest you to do some DDD so instead of simply doing an anemic class for Employee create a property that returns the composed user name.
class Employee
{
public string ComposedName
{
get {
return this.LastName + string.IsNullOrEmpty(this.preferedName) ?
this.FirstName : this.PreferedName;
}
}
}
To me that should be treat as a calculation and there is no need to do it in the SQL query. As a bonus this code can be Unit tested.