activerecord - select most recent message grouped by foreign key in Rails -

working on rails app. message table looks this:

message table

recipient_id | engagement_id

my goal show recent message of engagement, same recipient_id current_user, grouped engagement. post seems going for

finding recent entry per reference (foreign key) in rails

having trouble getting syntax correct. here's have currently:

select message,max(time) maxtime message group engagement_id

thanks in advance