How do I perform a LINQ Where operation on an object two layers deep and produce a flat list from it?

Question

I have an EF DB context query that produces a list of objects that look like this:

public interface Parent
{
    public string Name { get; set; }
    public virtual ICollection<Child> Children {get; set;}
}

public interface Child 
{
    public string Name {get; set;}
    public boolean isValid {get; set;}
}

The query itself looks like

var list _dbContext.Parents.Include(x => x.Children).ToList();

I want to be able to query each parent, pull out the details of each child that has isValid = true and then store them all in a list, but I can't figure out the syntax.

I was trying to do something like

list.Where(x => x.Children.Where(child => child.isValid).toList()).toList();

But the above just produces an IList<IList>

Answer 1

I've accomplished that using an expression like this:

var list.Where(x => x.Children.Any(child => child.isValid)).toList();

Keyword Any is very powerful in this cases