Recursive Hierarchy - Recursive Query using Linq

I am using Entity Framework (version 6) to map to a recursive hierarchy and it maps nicely.

My issue is that I want to recursively get ALL child nodes of a particular node in the hierarchy.

I get the child nodes quite easily using Linq:

var recursiveList = db.ProcessHierarchyItems
            .Where(x => x.id == id)
            .SelectMany(x => x.Children);

Does anybody know of a clean implementation, that will recursively get all children?

Solution

While it is possible to use a recursive method here, you can traverse this tree structure using an explicit stack instead to avoid using the stack space, which isn't always sufficient for large tree structures. Such a method is also very nice as an iterator block, and iterator blocks are much more expensive when recursive than regular methods, so this will perform better as well:

public static IEnumerable<T> Traverse<T>(this IEnumerable<T> items, 
    Func<T, IEnumerable<T>> childSelector)
{
    var stack = new Stack<T>(items);
    while(stack.Any())
    {
        var next = stack.Pop();
        yield return next;
        foreach(var child in childSelector(next))
            stack.Push(child);
    }
}