NHibernate - join without a mapping

Question

I'm aware that similar question have been asked here and here and it could probably be a duplicate.

But the question has not been answered in both the places properly so reluctantly, I have to ask it again :(

The question is can you use Criteria API to join two tables when there is no mapping available between them.

E.g

class Order{ UserId , OrderId} 
 class User{UserId , UserName}

and I need to produce a query like,

select user.UserName , order.OrderId from Order order join User user on order.UserId = user.UserId

Please help if anyone is aware of this..and please do note that I need to do it using Criteria or QueryOver techniques

Thanks /BB

Answer 1

Here is an idea on how it can be done but it is a bit ugly.

Since the mapping does not state that the relationship between Order and User exists therefore it is pretty difficult to have NHibernate generate a join between these two tables. What you can do instead is do an inner select so your query as SQL would look like this:

SELECT o.OrderId, o.WhateverOtherPropertyNameFromOrder
       (SELECT u.UserName, u.WhateverOtherPropertyNameFromUser
        FROM   User u
        WHERE  u.UserId = o.UserId)
FROM   Order o

This can be done like this on QueryOver:

Order order = null;
User user = null;

QueryOver<User> query = QueryOver.Of<User>(() => user)
    .Select(Projections.ProjectionList()
               .Add(Projections.Property<User>(x => x.UserName)))
               .Add(Projections.Property<User>(x => x.WhateverOtherPropertyNameFromUser)))
    .Where(Restrictions.EqProperty("user.Id", "order.UserId"));

var result = session.QueryOver<Order>(() => order)
    .Select(Projections.ProjectionList()
            .Add(Projections.Property<Order>(c => c.OrderId))
            .Add(Projections.Property<Order>(c => c.WhateverOtherPropertyNameFromOrder))
            .Add(Projections.SubQuery(query)))
    .List<object[]>();

I have no idea if this is useful at all to you but it is a potential solution to your problem.