I asked myself the same question when I was working through this new merge process. I believe it should be a has_one relationship, but for some reason, it was declared as a has_many here.  I looked in the schema and the db and there is no index declared on it to make person_id unique (like I see with other tables). 
    Is there a standard we should use of where this type of relationship is defined? I ask because I saw that for sp_user, which is a has_one, there is an index declared to make the user_id unique and so we declare it as a has_one relat.  For person_access, this is not true, so I figured someone decided this, maybe not thinking it through.  Anyway, since it is done, can we just declare it as a has_one in all the Person model files and that is good enough?  Or do we need to do a migration to add an index to it?  Or should we leave it alone at this point?