Question

I have a database with 2 tables:

1. Items
2. ItemDependencies

Items has key of ID

ItemDependencies have two columns: ItemId, and DependsOnItemId

I conver this to a collection:

 IEnumerable<Item> items = GetItems();

each item has a: Dependencies property which is a

List<Item>

So i want to filter the initial items list to:

1. Given a single item, i want a list of that item and all of the items that dependon this item recursively.

2. Given a single item, i want a list of that item and all of the other items that it depends on (also recursively).

what is the best way of doing this in C#, LINQ, or anything else that would do the trick.

Answer 1

To get a list of all the dependencies of an element you can use the following recursive function:

IEnumerable<Item> GetAllDependencies(Item i)
{
    IEnumerable<Item> a = new Item[] { i };
    IEnumerable<Item> b = i.Dependencies
                           .SelectMany(d => GetAllDependencies(d))
                           .Distinct();
    return a.Concat(b);
}

This method assumes that there are no cycles in the dependency chain (if there is a cycle it will call itself recursively until it throws a StackOverflowException).

To do the reverse I’d suggest building a new data structure to hold the reverse-dependencies and then reuse the same technique.