LINQ Fluent NHIBERNATE .Contains() does not work in QueryOver<> but works in Query<>

Question

Using FNH, i am trying to retrieve categories, using the following:

_session.QueryOver<Data.Model.Category>()                                      .Where(c => tourCreateRequest.Categories.Contains(c.CategoryId))                                      .List()                                      .Select(_categoryMapper.CreateCategory)                                      .ToList(); 

But I get an error at the .Contains() method :

Unrecognised method call: System.Collections.Generic.ICollection`1[[System.Int64, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]:Boolean Contains(Int64)

Why am I getting that error, what is wrong?

I went through some posts, and then changed my query to (below), and this works with Query<>.

_session.Query<Data.Model.Category>()                                      .Where(c => tourCreateRequest.Categories.Contains(c.CategoryId))                                      .ToList()                                      .Select(_categoryMapper.CreateCategory)                                      .ToList(); 

I thought QueryOver<> is the latest and greatest and should be used instead of Query<>.

What is the issue with the way I am using QueryOver<> as shown above?

Answer 1

I found the answer. Thanks to the post at: NHibernate using QueryOver with WHERE IN

var categories = _session.QueryOver<Data.Model.Category>()                                      .WhereRestrictionOn(c => c.CategoryId).IsIn(ArrayofCategoryIds)                                      .List()                                      .Select(_categoryMapper.CreateCategory)                                      .ToList(); 

I had to use the WhereRestrictionOn()

Answer 2

This is tangentially related issue and this seemed like the best place to put it.

_session.Query<SomeType>.Where(t => someEnumerable.Contains(t)) 

was not working.

In my case someEnumerable was NOT a List<SomeType>, but rather a HashSet<SomeType>. Apparently, NH really wants it to be a list. So, I did this instead and it worked.

var someEnumerableList = someEnumerable.ToList(); _session.Query<SomeType>.Where(t => someEnumerableList.Contains(t) 

Also, FWIW, I was under the impression that Query<T> was the new preferred way to go and that QueryOver<T> was the less preferred way, because Query<T> returns IQueryable, meaning that it should be a little easier to test, and theoretically swap out ORMs.