Linq query list contains a list

Question

I have 2 a class's:

public class ObjectA
{
    public int Id;
    public string Name;
}

public class ObjectB
{
    public int Id;
    public string Name;
    public List<ObjectA> ListOfObjectA;
}

So I have two lists: One of ObjectB (ListObjectB) and Another contains a list of id's of ObjectA (called ListOfIdsA). If this i want to get a list of ObjectB where ObjectB.ListOfObjectA is in the ListOfIdsA.

My first (and wrong) approach was

ListObjectB.Where(p=> ListOfIdsA.Contains(p.ListOfObjectA.Select(b=>b.Id)))

But this obviously trows an exception. I google it, stackoverflowed, but I'm thinking that my search skills aren't going so well in this, can anybody give a ninja awser of this? (Prefereably in lambda expression)

Answer 1

If I understand the question correctly, you're looking for Intersect, with your own IEqualityComparer. Remember to correctly implement GetHashCode in the comparer.

Answer 2

Are you trying to get a list of ObjectBs where all of the ObjectAs are in ListOfIdsA, or any of them?

I think you want either:

ListObjectB.Where(p => p.ListOfObjectA.Any(x => ListOfIdsA.Contains(x.Id)))

or

ListObjectB.Where(p => p.ListOfObjectA.All(x => ListOfIdsA.Contains(x.Id)))

(You may well want to make ListOfIdsA a HashSet<string> if it's of significant size, btw.)