has_many :through questions

rubyonrails-talk
1

I've created the following associations using :through:

    class Person < ActiveRecord::Base       has_many :attendees, :dependent => :destroy       has_many :events, :through => :attendees, :uniq => true     end

    class Event < ActiveRecord::Base       has_many :attendees, :dependent => :destroy       has_many :people, :through => :attendees, :uniq => true     end

    class Attendee < ActiveRecord::Base       belongs_to :event       belongs_to :person     end

The database tables are as follows:

ActiveRecord::Schema.define(:version => 3) do

  create_table "attendees", :id => false, :force => true do |t|     t.column "event_id", :integer     t.column "person_id", :integer     t.column "bit_flags", :integer   end

  add_index "attendees", ["event_id"], :name => "index_attendees_on_event_id"   add_index "attendees", ["person_id"], :name => "index_attendees_on_person_id"

  create_table "events", :force => true do |t|     t.column "name", :string     t.column "description", :text     t.column "event_date", :date     t.column "start_time", :time     t.column "end_time", :time     t.column "last_register_date", :date     t.column "location_city", :string     t.column "location_state", :string, :limit => 2     t.column "location_zip", :string, :limit => 9     t.column "location_addr", :text     t.column "agenda", :text     t.column "contacts", :text   end

  create_table "people", :force => true do |t|     t.column "first_name", :string     t.column "last_name", :string     t.column "title", :string     t.column "organization", :string     t.column "email", :string     t.column "phone1", :string     t.column "phone2", :string   end

end

I wanted to use the following method which the documentation indicates is available for has-many associations. (See (http:// rails.rubyonrails.com/classes/ActiveRecord/Associations/ ClassMethods.html) :

    collection=objects - replaces the collections content by deleting and adding objects as appropriate.

That's because I want to eliminate redundant join records, i.e., there should be only one record in the attendees table that contains the combination of event_id=1 and person_id=1. I took "deleting and adding objects _as appropriate_" to mean that. Is this true?

Secondly, trying this code in class PeopleController:

    @person.events = Event.find(@params[:event_ids]) if params[:event_ids]

resulted in the following error:

    undefined method `events=' for #<Person:0x6836228>

So, did I get something wrong or is this method not available with :through associations?

If not available, is there another (best?) method or combination that would maintain the attendees table so that event_id + person_id combinations are unique?

btw, I also tried the following:

    @person.events << Event.find(params[:event_ids]) if params[:event_ids]

It works, but adds (appends) join records without regard to uniqueness.

Thanks, Stan

2

I solved as follows (not sure it's the best approach):

  def create     @person = Person.new(params[:person])     @events = params[:event_ids] if params[:event_ids]

    # Create attendee record for each selected event     if @person.save       if @events != nil then         @events.each { |event|           @person.events.push (Event.find(event))         }       end       flash[:notice] = 'Person was successfully created.'       redirect_to :action => 'list'     else       render :action => 'new'     end   end

  def update     @person = Person.find(params[:id])     @events = params[:event_ids] if params[:event_ids]     if @events != nil then       @events.each { |event|         if !Attendee.exists?(:person_id => @person, :event_id => event)           @person.events.push (Event.find(event))         end       }     end

    if @person.update_attributes(params[:person])       flash[:notice] = 'Person was successfully updated.'       redirect_to :action => 'show', :id => @person     else       render :action => 'edit'     end   end