Question

If I have an object with a parent child relationship with Id and ParentId representing the unique Id of the record and the Parent Id of the record.

I need a query that will query a list of objects and return the path to the root of the relationship for each item (i.e. Path = (AllTheParentNames)\ Name ).

Any help with this would be appreciated.

MyObject

int Id
int? ParentId
string Name
string Path

Answer 1

Is this the expected result?

class A
{
    public int Id;
    public int? ParentId;
    public string Name;


    public static Func<T1, T2> Fix<T1, T2>(Func<Func<T1, T2>, Func<T1, T2>> f)
    {
        return f(x => Fix(f)(x));
    }

    public static string[] GetPaths(A[] array)
    {
        return array.Select(
            Fix<A, string>(self => x => x.ParentId != null ? self(array.First(a => a.Id == x.ParentId.Value)) + "\\" + x.Name : x.Name)
            ).ToArray();
    }
}

it’s impossible to make in single query without recursion (foreach (Aggregate) on array may be good for simulate recursion, but it’s stupid)

Fix – is the Fixed point combinator