I am porting a Rails app to Rails 4.2. This Rails app contains some rather complex manual SQL code in associations - partly due to DB optimizations (e.g. subselects instead of JOINs), partly due to...

In my application, a user has_many tickets. Unfortunately, the tickets table does not have a user_id: it has a user_login (it is a legacy database). I am going to change that someday, but for now t...