How to convert this sql into named_scope

rubyonrails-talk
1

hi, i have a sql statement which has a subquery on itself. it gets all the unique invitees of a given event from table invitation. i came up with the sql but i don't know how to convert it into a named_scope which i can reuse in other places. please help.

sql:

select * from invitations inv join (select event_id, user_id, max(invite_time) as last_invite_time from invitations group by event_id, user_id) as last_inv on inv.event_id = last_inv.event_id and inv.user_id = last_inv.user_id and inv.invite_time = last_inv.last_invite_time and inv.event_id = @event_id

thanks batterhead

2

Correct me if I’m wrong, but can’t that query be rewritten as follows:

select event_id, user_id, max(invite_time) as last_invite_time from invitations where event_id = @event_id

group by event_id, user_id

Basically you want to get distinct event_id and user_id and the latest invite_time? No need to join to itself.

In that case, you could go ahead and do it like this in ActiveRecord:

Invitation.select(“event_id, user_id, max(invite_time) as last_invite_time”).group(“event_id, user_id”).where(:event_id => @event_id)