That gives an `AssociationTypeMismatch`.

If it did work I'd expect it to destroy the documents themselves (and the corresponding rows in the join table). I'd rather write `@group.memberships.destroy(document_id: document_ids)` (which I didn't consider, as passing args to `#destroy` isn't really on my radar) or my SQL version. Calling `#destroy` on `#memberships` doesn't work either though.

I'm not a big fan of the SQL snippet building that passing hashes of stuff into AREL methods does for you. I've seen it cause people problems in the past (whereas SQL snippets are very obvious in their intent), so I just see it as an oft pointless obfuscation. But I'll change it to this:

    @group.memberships.where(document_id: document_ids).destroy_all