Hierarchy Problem -> Replace Recursion with Linq Join?

Question

I have a self referential table, which has ID, ParentID (nullable).

So, the table contains many nodes, each node could be the root in the hierarchy (parent is null),

Answer 1

Basically I'm going with something like this as discussed in the SO link you proivded.

public IQueryable GetCategories(Category parent)
{
    var cats = (parent.Categories);
    foreach (Category c in cats )
    {
        cats  = cats .Concat(GetCategories(c));
    }
    return a;
}

CTEs are probably the best solution but I'd like to keep things all in the same tier for now.