Question

I’m trying to write a little Messagecenter for my Project.

The problem I’m running into is that I only want to show the very last message from or to user, the one which came last will be shown.

The Table has a ID a Sender_ID, Receiver_ID and a MessageTXT.

Until now I have used:

@messages = Message.find_by_sql("select * from messages where id IN(SELECT MAX( id ) FROM messages WHERE sender_id = #{current_user.id} OR receiver_id = #{current_user.id} GROUP BY sender_id, receiver_id )")

Which gives me the last message to and the last message from a different user.

Answer 1

You should be able to do this with a named scope and not have to use find_by_sql which is really a last-resort tool.

Example:

class Message < ActiveRecord::Base
  scope :for_user, lambda { |user_id|
    where([ 'sender_id=? OR receiver_id=?', user_id, user_id)
  }
end

Using this you can retrieve the last one:

@last_message = Message.for_user(user_id).order('id DESC').first

That should generate a query similar to what you have defined.