LINQ to nHibernate - translating SQL "NOT IN" expression to LINQ - linq-to-nhibernate

Question

I tried to translate SQL "NOT IN" expression to LINQ, and I found that I should use the "Contains" option.
I have 2 tables:
ProductsGroups Products
-------------- ---------
id product_id
product_id product_name
My queries looks like this:
var innerQuery = from pg in Session.Query<ProductsGroups>
select pg.product_id;
var Query = from p in Session.Query<Products>
where !innerQuery.Contains(p.product_id)
select new {p.product_id, p.product_name};
But the sql that nHibernate generates is wrong:
select p.product_id, p.product_name
from Products p
where not (exists (select product_id
from ProductsGroups pg
where p.product_id = pg.id))
The "where" clause is not on the right field, it compares product_id to progucts group id.
Does anybody knows how can I solve it?
The solution that I found for meanwhile is to convert first query to list, and then
use this list in second query:
var innerQuery = (from pg .....).ToList();
Then, the nHibernate translates the "Contains" expression to "NOT IN", as I want:
select p.product_id, p.product_name
from Products p
where not (p.product_id in (1,2,3,4))

Answer 1

I am not sure, but I think you're running into a problem b/c contains determines if an element is in the collection by "using the default equality comparer." (MS documentation) I assume your productgroup mapping specifies it's Id as the Id property. So from nHibernate's perspective that is the value to use to determine equality.