Question

I’ve crafted two queries which both work fine, but I am really struggling to understand how to combine them. I think my biggest issue is the fact that I’ve used two different syntax for the queries, but I wasn’t sure how to express my first query without using the “SQL-esque” mark-up.

List<Task> tasksFromQueue = NHibernateSession.CreateQuery(
    "Select t from Task t, QueueLocation q where q.Queue.ID = :queueID and (t.SiteID = q.ComponentID or t.OriginalSiteID = q.ComponentID)")
    .SetParameter("queueID", queueID).List<Task>().ToList();

List<Task> tasksFromWorkflow = NHibernateSession
    .CreateCriteria(typeof(Task), "Task")
    .CreateCriteria("Task.Order", "Order")
    .CreateAlias("Task.TaskDevice", "TaskDevice").List<Task>();

IEnumerable<Task> tasks = tasksFromWorkflow.Intersect(tasksFromQueue);

As you can see I have two issues:

• Using verbose syntax for the first query and the NHibernate mark-up for the second query.
• Hitting the DB twice and then intersecting the results.

The tasksFromWorkflow query is actually a lot more complicated than seen above. If you’d like to see the whole query click here. I wasn’t sure if the extra code really changed anything about my problem — so I decided to keep the immediately displayed snippet as short as possible while still explaining the problem.

I read that NHibernate doesn’t support intersection, so perhaps it isn’t possible to achieve in one query without becoming extremely convoluted?

Answer 1

i dont know how performant this will be but the idea should be clear

var tasksFromQueue = DetachedCriteria.For<Task>()
            .Add(Restrictions.Or(
                Subqueries.In("SiteID", DetachedCriteria.For<QueueLocation>().Add(Restrictions.Eq("Queue.ID", queueID)).SetProjection(Projections.Property("ComponentID"))),
                Subqueries.In("OriginalSiteID", DetachedCriteria.For<QueueLocation>().Add(Restrictions.Eq("Queue.ID", queueID)).SetProjection(Projections.Property("ComponentID")))))
            .SetProjection(Projections.Id());

    "Select t from Task t, QueueLocation q where q.Queue.ID = :queueID and (t.SiteID = q.ComponentID or t.OriginalSiteID = q.ComponentID)")
    .SetParameter("queueID", queueID).List<Task>().ToList();

var tasksFromWorkflow = DetachedCriteria.For<Task>()
    .CreateAlias("Order", "order")
    .CreateAlias("TaskDevice", "device")
    .Add(<restrictions>)
    .SetProjection(Projections.Id());

var results = NHibernateSession.CreateCriteria<Task>()
    .Add(Subqueries.In("Id", tasksFromQueue))
    .Add(Subqueries.In("Id", tasksFromWorkflow))
    .List<Task>();