Comment 9 for bug 1796945

I think the branch posted has the right idea, but as noted, is not going to be right in some cases. Even 'has_a' doesn't necessarily mean an inner join if the data allows the link to be null. (has_a only determines "direction" of the link)

Ultimately we're going to need to pull out the defined joins from the old structure if we really want to do a true conversion, since even if we improve the default logic, the old interface allowed one to override that default and set the join manually. Pulling out the old data didn't seem obvious after looking at least one bug back, but I am not yet familiar with the structural changes.