Fluent LINQ - Select a list of parents that contains a list of children where a subset of children are present

Question

That title is the worst...

Anyway, what I'm trying to do is select a parent object, who contains n number of child objects. I will be passing in a list of criteria (1..n) that the child objects have to match. For the sake of brevity, here's the classes i'm working with:

public class Parent {

     public int Id { get; set; }

     public List<Child> Children { get; set; }

}

public class Child { 

    public int Id { get; set; }

    public int ParentId { get; set; }

    public int SomeValue { get; set; }

}

What I'm looking for is a list of parents that contain children that match all of the SomeValues i'm passing in

So if I have:

Parent 1
    Child 1, SomeValue 10
    Child 2, SomeValue 20
    Child 3, SomeValue 40
Parent 2
    Child 4, SomeValue 10
    Child 5, SomeValue 20
    Child 5, SomeValue 50

and myList is [10, 50], it needs to return Parent 2 only. If myList is [10, 20] then both parents should be returned. And finally, if myList is [10, 20, 60], nothing should be returned.

I don't think the following will work, because the values that children has that aren't in the list will remove it from the results (right?)

parents.where(p => p.children.all(c => myList.contains(c.SomeValue)));

and an any won't work, because it will just return anything as long as one of its children matches. I need to ensure that the parent has a child that matches every item in myList. I also thought about adding a count to make sure the matched items were at least as large as the myList.length, but that might not work because SomeValue doesn't have to be distinct in the collection of children (I guess i could run a distinct subselect on the children's SomeValues?)

Answer 1

You can flip your condition, and check to make sure all of the list values are contained within the Children collection:

var matches = parents.Where(p => myList.All(v => p.Children.Select(c => c.SomeValue).Contains(v)));