# stick this method in project.rb
def self.list_of_person_ids_who_are_participants_and_belong_to_an_activity(project_id)
  joins = "JOIN activities ON activities.project_id = projects.id "
  joins << "JOIN activity_executions ON activity_executions.activity_id = activities.id"

  conditions = ["projects.id = ? ", project_id]

  find( :all,
        :select => 'activity_executions.person_id',
        :conditions => conditions,
        :joins => joins)
end

# go to ruby script/console and perform following operation
>> Project.list_of_person_ids_who_are_participants_and_belong_to_an_activity(1)

# I get following error from auto_escape
>> Project.list_of_person_ids_who_are_participants_and_belong_to_an_activity(1)
  Project Load (0.000929)   SELECT activity_executions.person_id FROM `projects` JOIN activities ON activities.project_id = projects.id JOIN activity_executions ON activity_executions.activity_id = activities.id WHERE (projects.id = 1 )
  Project Columns (0.003555)   SHOW FIELDS FROM `projects`
NoMethodError: You have a nil object when you didn't expect it!
The error occurred while evaluating nil.text?
    from /Users/nkumar/work/community_service/vendor/plugins/auto_escape/lib/auto_escape.rb:57:in `after_find'
    from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/set.rb:231:in `delete_if'
    from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/set.rb:231:in `delete_if'
    from /Users/nkumar/work/community_service/vendor/plugins/auto_escape/lib/auto_escape.rb:57:in `after_find'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/callbacks.rb:301:in `send'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/callbacks.rb:301:in `callback'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:1446:in `send'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:1446:in `instantiate'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:582:in `find_by_sql'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:582:in `collect!'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:582:in `find_by_sql'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:1341:in `find_every'
    from /Library/Ruby/Gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:536:in `find'
    from /Users/nkumar/work/community_service/app/models/project.rb:321:in `list_of_person_ids_who_are_participants_and_belong_to_an_activity'
    from (irb):8