I think its a bug and not going to be supported by Subsonic. I had the same issue when doing other things here
Jon
2009-07-16 11:49:30
I have a fork for left join that I'll be pulling in the next few days - gimme a week and I'll push another release with this.
t seems there still isn't a fix in place for this. A simple fix (dirty one albeit) is to create a view that handles the left join and fills the empty data from the right with default data and have SubSonic do a simple join on that view.
I know it's terrible but its a fix for now. I couldn't see dropping SubSonic due to this limitation. I'm sure it will be fixed soon.