Filtering IQueryable sub list

Question

Working with Entity Framework, but that\'s probably irrelevant If I have an Iqueryable, how do I filter a sub list and keep it IQueryable so it doesn\'t yet hit the DB?

Answer 1

If you want to filter children down to where there's only one child per parent, you need to start with children, select their parents, and do not touch the parents' subitems:

IQueryable childItems = context
    .SubItems.Include("Item")
    .Where(si => si.Id == 1 && si.Item.SomeAttr == someValue);
//               ^^^^^^^^^^    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//                   |                         |
//                   |           Set a condition on the parent
//  Set a condition on the child

I assume that each sub-item has a link "pointing" back at its parent.