Non-optimal sql

I was noticing that to update a has_many association, Rails uses the

delete from tagpairs where id = 33;
delete from tagpairs where id = 34;
delete from tagpairs where id = 35;

insert into tagpairs (…) values (…);
insert into tagpairs (…) values (…);


This would be better as:

delete from tagpairs where obj_type = 'guidepage' and obj_id = 1;
insert into tagpairs (...) values (...);

In my case, I’m using a polymorphic association. However, the basic
idea applies to a non-polymorphic association. We can and should delete
members of the association based on the association key field having a
certain value rather than deleting specific ids. Also, notice how this
means that we don’t necessarily have to store the ‘id’ field, which, for
my application, is redundant.