Multi Select menus and Virtual Attributes

I have periods table that has start_at:datetime end_at:datetime . Because each period begins and end at the same date, I want to separate the in three fields instead of two.

field 1: the date field 2: the time "00:00" of start field 3: the time "00:00" of end

I started and done this. But unfortunately, I faced a problem.

So please take a look at the period model, the form and the error, and correct me, correct the code.

Thanks in advance!

Period model

class Period < ActiveRecord::Base
  belongs_to :show

  def show_date; start_at.nil? ? Time.now.to_date : start_at.to_date; end
  def start_at_time; start_at.nil? ? Time.now.to_time : start_at.to_time; end
  def end_at_time; end_at.nil? ? Time.now.to_time : end_at.to_time; end

  def start_at_time=(start_str)
   self.start_at = DateTime.parse("#{show_date.strftime("%Y-%m-%d")}T#{start_str.strftime("%H:%M:%S")}")
  end

  def end_at_time=(end_str)
   self.end_at = DateTime.parse("#{show_date.strftime("%Y-%m-%d")}T#{end_str.strftime("%H:%M:%S")}")
  end
end

Periods schema

#just the schema for periods table
  create_table "periods", :force => true do |t|
    t.integer "show_id"
    t.datetime "start_at"
    t.datetime "end_at"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

_form.html.erb

  <div class="group">
    <%= f.label :show_id, "Show", :class => :label %>
    <%= f.collection_select :show_id, @shows.开发者_如何学编程collect, :id, :name %>
    <span class="description">Select the show</span>
  </div>

  <div class="group">
    <%= f.label :show_date, "Date at", :class => :label %>
    <%= f.date_select :show_date, :class => 'datetime_select' %>
    <span class="description">Date of the show</span>
  </div>

  <div class="group">
    <%= f.label :start_at_time, "Start at", :class => :label %>
    <%= f.time_select :start_at_time, {:minute_step => 15, :ignore_date => true}, :class => 'datetime_select' %>
    <span class="description">Time :: When does it start?</span>
  </div>

  <div class="group">
    <%= f.label :end_at_time, "End at", :class => :label %>
    <%= f.time_select :end_at_time, {:minute_step => 15, :ignore_date => true}, :class => 'datetime_select' %>
    <span class="description">Time :: When does it end?</span>
  </div>

  <div>
    <button class="button" type="submit"><%= image_tag("tick.png", :alt => "Save") %> Save</button>
  </div>

The Error

==Framework Trace 

3 error(s) on assignment of multiparameter attributes



==Framework Trace 

/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:3073:in `execute_callstack_for_multiparameter_attributes'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:3028:in `assign_multiparameter_attributes'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:2750:in `attributes='
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:2628:in `update_attributes'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:1331:in `send'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:1331:in `perform_action_without_filters'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/filters.rb:617:in `call_filters'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/filters.rb:610:in `perform_action_without_benchmark'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/home/amrnt/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/usr/lib/ruby/1.8/benchmark.rb:308:in `realtime'
/home/amrnt/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/rescue.rb:160:in `perform_action_without_flash'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/flash.rb:146:in `perform_action'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:532:in `send'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:532:in `process_without_filters'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/filters.rb:606:in `sass_old_process'
/usr/lib/ruby/gems/1.8/gems/haml-2.3.0/lib/sass/plugin/rails.rb:19:in `process_without_compass'
/home/amrnt/cc/vendor/gems/compass-0.8.17/lib/compass/app_integration/rails/action_controller.rb:7:in `process'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:391:in `process'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb:386:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/routing/route_set.rb:437:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:87:in `dispatch'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:121:in `_call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:130:in `build_middleware_stack'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/query_cache.rb:29:in `call'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/query_cache.rb:29:in `call'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/connection_adapters/abstract/query_cache.rb:34:in `cache'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/query_cache.rb:9:in `cache'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/query_cache.rb:28:in `call'
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:361:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/string_coercion.rb:25:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/head.rb:9:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/methodoverride.rb:24:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/params_parser.rb:15:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/session/cookie_store.rb:93:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/failsafe.rb:26:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `synchronize'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/lock.rb:11:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:114:in `call'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/reloader.rb:34:in `run'
/home/amrnt/.gem/ruby/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:108:in `call'
/usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/rails/rack/static.rb:31:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:46:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `each'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `call'
/usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/rails/rack/log_tailer.rb:17:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/content_length.rb:13:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/chunked.rb:15:in `call'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/handler/mongrel.rb:64:in `process'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:159:in `process_client'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in `each'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in `process_client'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `run'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `initialize'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `new'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `run'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `initialize'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `new'
/usr/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `run'
/home/amrnt/.gem/ruby/1.8/gems/rack-1.0.1/lib/rack/handler/mongrel.rb:34:in `run'
/usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/commands/server.rb:111
/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
script/server:3



==Request Parameters:

{"period"=>{"start_at_time(4i)"=>"20",
 "start_at_time(5i)"=>"00",
 "end_at_time(4i)"=>"23",
 "end_at_time(5i)"=>"30",
 "show_date(1i)"=>"2010",
 "show_date(2i)"=>"3",
 "show_date(3i)"=>"31",
 "show_id"=>"1"},
 "_method"=>"put",
 "authenticity_token"=>"pm/cXQQnOCsidcAj/OEJuMtHgfppZvoqq09epdETAxo=",
 "id"=>"46"}

The date and time form helpers included with ActionView generate special form elements that use something called "multiparameter assignment". It means when you submit the date_select, datetime_select or time_select form fields, they generate several separate parameters that are compiled by ActiveRecord into one date, datetime or time object. In your case, those parameters look like:

 "start_at_time(4i)"=>"20",
 "start_at_time(5i)"=>"00"

 "end_at_time(4i)"=>"23",
 "end_at_time(5i)"=>"30"

 "show_date(1i)"=>"2010",
 "show_date(2i)"=>"3",
 "show_date(3i)"=>"31"

I should note that these are very different from the strings you're expecting in your Period model's start_at_time= and end_at_time= methods and that your model doesn't have a show_date= method at all.

That parameter format, with parentheses, is what Rails uses for multiparameter assignment. However, ActiveRecord relies on a corresponding database column in order to know whether the multiple parameters submitted represent a date, time or datetime object. That means the helpers won't work on virtual attributes, at least out-of-the-box. There's no way to tell what kind of object they expect.

There's at least one active ticket on this:

https://rails.lighthouseapp.com/projects/8994/tickets/2675-support-for-multiparameter-attribute-assignment-on-virtual-attribute-writers

And you can find a great overview of multiparameter assignment and using date form helpers with Rails at this link:

http://www.alexrothenberg.com/2009/05/how-to-use-dates-in-rails-when-your.html

Regarding general improvement to this design: if every period starts and ends on the same date, why not use a date attribute to store the period date and two time attributes to store the start and end times. You could easily create a methods that return start_at and end_at datetime objects that are compiled from those attributes.

You can set up your form using the form helpers more or less as you already have. You could also easily set up a validation on the end_time attribute, ensuring it's always later in the day than the start_time.