Question

I have an object called Device. A Device can have one parent Device. A Device can also have n child Devices.

I have a drop down list that shows all the selectable Devices. I can get all the Devices in the database quite easily – db.Devices.

The hierarchy can be infinite levels deep.

I need to get all Devices that aren’t above or below a given Device in the tree. Essentially I’m asking for Devices unrelated to a given Device (neither a parent/grandparent/great grandparent/etc or a child/grandchild/great grandchild/etc). I also need to exclude the given Device from the list.

What is the best way to do this? Should I use recursion?

(I am using C# and Entity Framework with an SQL Server database, so I can use Linq To SQL or use the model itself.)

Answer 1

My approach would be first to get all of the siblings of the device D:

P = parent of the device
sibs = {all children of P that are not D}

Any descendants of any d in sibs is unrelated to D. Keep going up the family tree:

G = grandparent of the device
sibs = sibs union {all children of G that are not P}

Continuing this way, the set sibs and all their descendants is the set you’re after.

In pseudocode:

D = device;
siblings = {};
while (D has parent) {
    P = parent(D);
    siblings = siblings union (children(P) \ D);
    D = P;
}
return descendants(siblings);