Method syntax join onto ObjectQuery in LINQ to Entities

Question

For my client's sake, I have forgone pride and dignity and opted for the exampled means of choosing an entityset to select from, but I need to join this to another, fixed, entityset, and this challenge is beyond me today.

I need to project a set of attributes from both Department*n,* and another entity set called Sites. I can join Department1 and Sites, but I am stumped at joining oq to Sites to select a projection of fields from both.

Must I prostitute myself further, and repeat the entire query in each case of the switch statement?

        ExtensionsEntities ents = new ExtensionsEntities();
        ObjectQuery oq = null;

'#'region DirtySwitch

        switch (layerName)
        {
            case "Department1":
                oq = ents.Department1;
                break;
            case "Department2":