How to take this sql query and turn it into nhibernate query - sql

Question

I am trying take this sql query and make it into an nhibernate HQL query. I am using nhibernate 3 and Fluent Nhibernate 1.2
SELECT dbo.Tasks.CourseId, dbo.CoursePermissions.BackgroundColor, dbo.Tasks.DueDate, dbo.Tasks.TaskName, dbo.Tasks.TaskId
FROM dbo.Courses INNER JOIN
dbo.Tasks ON dbo.Courses.CourseId = dbo.Tasks.CourseId INNER JOIN
dbo.CoursePermissions ON dbo.Courses.CourseId = dbo.CoursePermissions.CourseId
WHERE (dbo.Tasks.CourseId = 1)
I would have liked to use linq but I don't think nhibernate supports linq joins yet so I guess I am stuck with using HQL(unless someone knows a better way).
I guess I can use QueryOver or the other ways nhibernate does queries so whatever works the best. I still don't understand the difference between all the ways as if I could do everything in linq I would.
However I have no clue on how to write my query.
Thanks
Edit
I now have this(changed a bit)
Course cAlias = null;
Task tAlias = null;
CoursePermission cpAlias = null;
var result = session.QueryOver<Task>(() => tAlias)
.JoinAlias(() => tAlias.Course, () => cAlias)
.JoinAlias(() => cAlias.CoursePermissions, () => cpAlias)
.Where(Restrictions.In(Projections.Property(() => cAlias.Id), courseIds))
.And(x => x.DueDate >= startDate)
.And(x => x.DueDate <= endDate)
.Select( Projections.Property(() => cAlias.Id),
Projections.Property(() => cpAlias.BackgroundColor),
Projections.Property(() => tAlias.DueDate),
Projections.Property(() => tAlias.TaskName),
Projections.Property(() => tAlias.TaskId))
.List<object[]>();
I know want to map it to
public class TaskAppointments
{
public int Id { get; set; }
public string BackgroundColor { get; set; }
public DateTime DueDate { get; set; }
public int TaskId { get; set; }
public string TaskName { get; set; }
}
How do I do this. If this was a linq method I would do
.Select(new TaskAppointments { TaskId = Projections.Property(() => tAlias.TaskId)})
but it says it can't convert it to an int.
Edit2
This is what I came up with
Course cAlias = null;
Task tAlias = null;
CoursePermission cpAlias = null;
TaskAppointments taskAppointments = null;
List<TaskAppointments> result = session.QueryOver<Task>(() => tAlias)
.JoinAlias(() => tAlias.Course, () => cAlias)
.JoinAlias(() => cAlias.CoursePermissions, () => cpAlias)
.Where(Restrictions.In(Projections.Property(() => cAlias.Id), courseIds))
.And(x => x.DueDate >= startDate)
.And(x => x.DueDate <= endDate)
.SelectList(list =>
list.SelectGroup(x => x.TaskId).WithAlias(() => taskAppointments.TaskId)
.SelectGroup(() => cpAlias.BackgroundColor).WithAlias(() => taskAppointments.BackgroundColor)
.SelectGroup(x => x.DueDate).WithAlias(() => taskAppointments.DueDate)
.SelectGroup(x => x.TaskName).WithAlias(() => taskAppointments.TaskName)
)
.TransformUsing(Transformers.AliasToBean<TaskAppointments>())
.List<TaskAppointments>().ToList();

Answer 1

Without mappings I assume that you have the following relationships: Courses -> Tasks (1:n) and Courses -> CoursePermissions (1:n)
I also assumed that you do not want the complete objects but only certain properties, so I used projections.
QueryOver version:
// the aliases are required here, so that we can reference the entities properly
Courses cAlias = null;
Tasks tAlias = null;
CoursePermissions cpAlias = null;
var result = session.QueryOver<Courses>(() => cAlias)
.JoinAlias(() => cAlias.Tasks, () => tAlias)
.JoinAlias(() => cAlias.CoursePermissions, () => cpAlias)
.Where(() => cAlias.CourseId == 1)
.Select(Projections.Property(() => cAlias.CourseId),
Projections.Property(() => cpAlias.BackgroundColor),
Projections.Property(() => tAlias.DueDate),
Projections.Property(() => tAlias.TaskName),
Projections.Property(() => tAlias.TaskId))
.List<object[]>();
Edit start
If you need to do a WHERE IN clause, you can do this:
List<int> courseIdList = new List<int>() { 1, 2 };
var result = session.QueryOver<Courses>(() => cAlias)
.JoinAlias(() => cAlias.Tasks, () => tAlias)
.JoinAlias(() => cAlias.CoursePermissions, () => cpAlias)
.Where(Restrictions.In(Projections.Property(() => cAlias.CourseId), courseIdList))
.Select(...)
.List<object[]>();
Edit end
Edit 2 start
If you want to transform it into a DTO:
// AliasToBeanResultTransformer is in namespace NHibernate.Transform
// we have to use .As("...") for the transformer to find the correct property-names
var result = ...
.Select(Projections.Property(() => cAlias.CourseId).As("CourseId"),
Projections.Property(() => cpAlias.BackgroundColor).As("BackgroundColor"),
Projections.Property(() => tAlias.DueDate).As("DueDate"),
Projections.Property(() => tAlias.TaskName).As("TaskName"),
Projections.Property(() => tAlias.TaskId).As("TaskId"))
.TransformUsing(new AliasToBeanResultTransformer(typeof(TaskAppointments)))
.List<TaskAppointments>();
Edit 2 end
HQL version:
string hql = "select c.CourseId, cp.BackgroundColor, t.DueDate, t.TaskName, t.TaskId"
+ " from Courses as c inner join c.Tasks as t inner join c.CoursePermissions as cp"
+ " where c.CourseId = 1";
var result2 = session.CreateQuery(hql)
.List<object[]>();
Be aware that this will result in a cartesian product, so for each Course you will get Tasks.Count + CoursePermissions.Count rows.