(the learning curve I have currently is like climbing a steep mountain of loose gravel)...

OK. I have a silverlight 4 app. EF datamodel of my SQL database. Domain DataService making my Entities visible.

Two entity tables are Projects and Change_Requests. Projects has primary key Project_ID. Change Requests has FK Product_ID. Change Requests have a SubdivisionID (int) field.
 
They seem to be functioning as entities correctly. The GetProjectsQuery and GetChange_RequestQuery queries seem to be functional (all built automatically when creating the datamodel and domainservice).

This works fine..

            EntityQuery<Project> query = (from P in _Context.GetProjectsQuery()
                                          where P.Proj_Name.Contains(txtFilterProjectName.Text.Trim())
                                          orderby P.Proj_Name
                                          select P);
            LoadOperation<Project> lo = _Context.Load<Project>(query);

            DataGridProjects.ItemsSource = lo.Entities;

GetChange_RequestQuery works ok too.

Now I'm trying to do the equivalent of a join or subquery to get Projects that have Change_Requests in a specific Change_Request.SubdivisionID.

I've tried..

            EntityQuery<Project> query = (from p in _Context.Projects
                                          from c in _Context.Change_Requests
                                          where p.Project_ID == c.Project_ID && c.Subdivision == SubdivisionID
                                          select p);

I get an error ..
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<ChangeManagement.Web.Project>' to 'System.ServiceModel.DomainServices.Client.EntityQuery<ChangeManagement.Web.Project>'

OK, let's try using the Getmethods (like the one that worked above)..

            EntityQuery<Project> query = (from p in _Context.GetProjectsQuery()
                                          from c in _Context.GetChange_RequestQuery()
                                          where p.Project_ID == c.Project_ID
                                              && c.Subdivision.Equals(SubdivisionID)
                                          select p);

Error..
Could not find an implementation of the query pattern for source type 'System.ServiceModel.DomainServices.Client.EntityQuery<ChangeManagement.Web.Project>'.  'SelectMany' not found.

OK  - let's try a join..
            EntityQuery<Project> query = (from p in _Context.Projects
                                          join c in _Context.Change_Requests on p.Project_ID equals c.Project_ID
                                          where c.Subdivision.Equals(SubdivisionID)
                                          select p);

Error..
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<ChangeManagement.Web.Project>' to 'System.ServiceModel.DomainServices.Client.EntityQuery<ChangeManagement.Web.Project>'

What am I missing?? Apparently working with more than one entity changes the query to IEnumerable rather than EntityQuery? 

How do I get by this?