Porting complicated has_many relationships to Rails >4.1 (without finder_sql)

Question

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

Answer 1

Pass the proc that contains the SQL string as scope.

has_many :internal_messages, -> { proc { "SELECT DISTINCT(internal_messages.id), internal_messages.* FROM internal_messages " +
      ' LEFT JOIN internal_messages_recipients ON internal_messages.id=internal_messages_recipients.internal_message_id' +
      ' WHERE internal_messages.sender_id = #{id} OR internal_messages_recipients.recipient_id = #{id}' } }