I’m currently working on a questionnaire system which has two main objects: Question and Questionnaire. I had been associating them using has_and_belongs_to_many, but a new requirement means that I now need to be able to define a question order within each questionnaire. <\/p>\n
act_as_list<\/a> gives me much of the functionality I want. However, I could not just add that to the Question model, because I may need a question to be at position 1 in one questionnaire, and position 4 within another.<\/p>\n The solution was to refactor the has_and_belongs_to_many association to use has_many :through. To do this I had to create a joining class. I called this new class QuestionnairesQuestion. Using a plural on the first word of the class name allowed me to use the has_and_belongs_to_many join table, so I wouldn’t lose the existing relationships.<\/p>\n The required migration took a little work. First I had to add in an id and make it a primary key (the existing table only had question_id and questionnaire_id fields). Then I also needed to generate some initial values for the new fields I was adding. This was my solution:<\/p>\n I then needed to add the acts_as_list declaration to QuestionnairresQuestion with a scope option so that sorting was per questionnaire. These are the associations that worked for me:<\/p>\n This worked, but I did have an issue with determining which question was top within each scope. The problem was that act_as_list assumes the top item will have the position ‘1’. However, I’d made the position match the id, which meant that at best only one item would have a position of ‘1’. To fix this I created this rake task:<\/p>\n Running that got the associations working. There is probably a better way of doing this, but this will do for now.<\/p>\n My next problem was how to access the act_as_list functionality. <\/p>\n If questions were the act_as_list object, you could do things like this<\/p>\n However, as questions are used on multiple questionnaires and they need to be independently sortable within each questionnaire, it is the through table model QuestionnairesQuestion that acts_as_list. To change position the change must be made in the context of the questionnaire.<\/p>\n My solution was to add these methods to Questionnaire:<\/p>\n pass_method_to_questionnaires_question<\/em> in combination with method_missing<\/em>, allows you to pass to a questionnaire the acts_as_list method together with the question it needs to effect. The equivalent move_higher call then becomes:<\/p>\n You can now also do:<\/p>\n I’m currently working on a questionnaire system which has two main objects: Question and Questionnaire. I had been associating them using has_and_belongs_to_many, but a new requirement means that I now need to be able to define a question order within … Continue reading
\n def<\/span> up
\n add_column :questionnaires_questions<\/span>, :id<\/span>, :primary_key<\/span>
\n add_column :questionnaires_questions<\/span>, :position<\/span>, :integer<\/span>
\n add_column :questionnaires_questions<\/span>, :created_at<\/span>, :datetime<\/span>
\n add_column :questionnaires_questions<\/span>, :updated_at<\/span>, :datetime<\/span>
\n
\n execute "UPDATE questionnaires_questions SET position = id, created_at = now(), updated_at = now()"<\/span>
\n end<\/span>
\n
\n def<\/span> down
\n remove_column :questionnaires_questions<\/span>, :id<\/span>
\n remove_column :questionnaires_questions<\/span>, :position<\/span>
\n remove_column :questionnaires_questions<\/span>, :created_at<\/span>
\n remove_column :questionnaires_questions<\/span>, :updated_at<\/span>
\n end<\/span>
\n
\nend<\/span><\/div><\/div>\n
\n
\n has_many :questionnaires_questions<\/span>
\n
\n has_many(<\/span>
\n :questionnaires<\/span>,
\n :through<\/span> =><\/span> :questionnaires_questions<\/span>,
\n :uniq<\/span> =><\/span> true<\/span>
\n )<\/span>
\nend<\/span>
\n
\nclass<\/span> Questionnaire <<\/span> ActiveRecord::Base<\/span>
\n
\n has_many(<\/span>
\n :questionnaires_questions<\/span>,
\n :order<\/span> =><\/span> 'position'<\/span>
\n )<\/span>
\n
\n has_many(<\/span>
\n :questions<\/span>,
\n :uniq<\/span> =><\/span> true<\/span>,
\n :through<\/span> =><\/span> :questionnaires_questions<\/span>,
\n :order<\/span> =><\/span> 'position'<\/span>
\n )<\/span>
\nend<\/span>
\n
\nclass<\/span> QuestionnairesQuestion <<\/span> ActiveRecord::Base<\/span>
\n
\n belongs_to :questionnaire<\/span>
\n belongs_to :question<\/span>
\n
\n acts_as_list :scope<\/span> =><\/span> :questionnaire<\/span>
\nend<\/span><\/div><\/div>\n
\n
\n # Usage: rake data:reset_positions RAILS_ENV=production<\/span>
\n desc "Goes through each of the acts_as_list objects and resets the positions based on order they were added to the database"<\/span>
\n task :reset_positions<\/span> =><\/span> :environment<\/span> do<\/span>
\n ActiveRecord::Base<\/span>.connection<\/span>.execute<\/span> "START TRANSACTION;"<\/span>
\n Questionnaire.all<\/span>.each<\/span> do<\/span> |<\/span>questionnaire|<\/span>
\n first_id = questionnaire.questionnaires_questions<\/span>.minimum<\/span>(<\/span>:id<\/span>)<\/span>
\n if<\/span> first_id # nil if questionnaire has no questions<\/span>
\n sql = "UPDATE questionnaires_questions SET position = (1 + id - #{first_id}) WHERE questionnaire_id = #{questionnaire.id};"<\/span>
\n ActiveRecord::Base<\/span>.connection<\/span>.execute<\/span> sql
\n end<\/span>
\n end<\/span>
\n ActiveRecord::Base<\/span>.connection<\/span>.execute<\/span> "COMMIT;"<\/span>
\n puts<\/span> "Positions reset"<\/span>
\n end<\/span>
\nend<\/span><\/div><\/div>\n
\n def<\/span> method_missing(<\/span>symbol, *<\/span>args, &<\/span>block)<\/span>
\n if<\/span> acts_as_list_method?(<\/span>symbol)<\/span>
\n pass_method_to_questionnaires_question(<\/span>symbol, args.first<\/span>)<\/span>
\n else<\/span>
\n super<\/span>
\n end<\/span>
\n end<\/span>
\n
\n def<\/span> pass_method_to_questionnaires_question(<\/span>symbol, question)<\/span>
\n raise<\/span> "A Question is needed to identify QuestionnairesQuestion"<\/span> unless<\/span> question.kind_of<\/span>? Question
\n questionnaires_question = questionnaires_questions.where<\/span>(<\/span>:question_id<\/span> =><\/span> question.id<\/span>)<\/span>.first<\/span>
\n questionnaires_question.send<\/span>(<\/span>symbol)<\/span> if<\/span> questionnaires_question
\n end<\/span>
\n
\n def<\/span> acts_as_list_method?(<\/span>symbol)<\/span>
\n ActiveRecord::Acts::List::InstanceMethods<\/span>.instance_methods<\/span>.include<\/span>?(<\/span>symbol.to_sym<\/span>)<\/span>
\n end<\/span><\/div><\/div>\n
\nquestionnaire.last<\/span>?(<\/span>question)<\/span><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"