LINQ Query - Complicated Self Join Problems

So I have Projects (for t开发者_JS百科his example say they are a Name and an ID). I also have a table called SubProjects, like this:

MasterProjectID       SubProjectID
1                     2
1                     3
4                     5
4                     6
4                     7

A master cannot be a sub of another master.

I want to return a list of project IDs. Specifically, I want the list to contain the Master project ID and all of its Sub project IDs.

In other words, if projectID == 4 and pdc is my DataContext, my query should return:

4
5
6
7

The following linq query returns nothing:

   from j in pdc.Projects
   join s in pdc.SubProjects on j.ProjectID equals s.SubProjectID
   where j.ProjectID.Equals(projectID) || s.MasterProjectID.Equals(projectID)
   select j.ProjectID;

What am I doing wrong?

You could retrieve a list of sub-projects simply with:

var query = from j in pdc.SubProjects
            where j.MasterProjectID == projectID
            select j.SubProjectID;

... Then manually append/prepend the known value of projectID.

var list = query.ToList();
list.Add(projectID);