Ash should automatically define join resources for many-to-many relationships.

[jimsynz]

This one is a bit weird, because if the data layer isn't postgres do we even need a join resource? if both sides are ETS backed (for example) then can we just store arrays or something?

[zachdaniel]

It would be less simple IMO not more simple to have a special route for simpler data layers, because often join resources end up getting behavior like fields/policies/actions.