Question

I’m using a datetime to save some appointments in a calendar.
In this way I can store togheter date and time without have the two values distinct.

What I’d like is to allow users to edit the appointment and change date/time.
The fact is that I cannot leave the user free to select any hour but any appointment must be set in a predefined range of hours (24h format: 10, 12, 14, 16, 18, 20).

Since in the documentation I could not find any way to customize datetime_select I’m actually using the following form:

.control-group
  = f.label :start_at, :class => 'control-label'
  .controls
    = f.date_select :start_at, :value => f.object.start_at, :class => "datetimefield"
.control-group
  = f.label :start_at, :class => 'control-label'
  .controls
    = f.select :start_at, :value => Event::ALLOWED_HOURS, :class => 'number_field'

Event::ALLOWED_HOURS is an array containing the hours I want to let users choose from.
When submitting this form the update action loses the timing info, resulting in a datetime like: 2012-05-18 00:00:00 instead of using the hour defined in my select.

What can I do to make this work as I need?

This is the controller, please note that this is a nested resource of EventCalendar:

class EventsController < ApplicationController
  before_filter :authenticate_user!
  load_and_authorize_resource

  # GET /events
  # GET /events.json
  def index
    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @events }
    end
  end

  # GET /events/1
  # GET /events/1.json
  def show
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @event }
    end
  end

  # GET /events/new
  # GET /events/new.json
  def new
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
    @start_at = Time.parse("#{params[:day]} #{params[:hour]}")
    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @event }
    end
  end

  # GET /events/1/edit
  def edit
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
  end

  # POST /events
  # POST /events.json
  def create
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
    @start_at = params[:start_at]

    respond_to do |format|
      if @event.save
        format.html { redirect_to root_path, notice: 'Appuntamento creato con successo.' }
        format.json { render json: @event = EventCalendar.find(params[:event_calendar_id]), status: :created, location: @event }
      else
        format.html { render action: "new" }
        format.json { render json: @event.errors, status: :unprocessable_entity }
      end
    end
  end

  # PUT /events/1
  # PUT /events/1.json
  def update
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
    respond_to do |format|
      if @event.update_attributes(params[:event])
        format.html { redirect_to root_path, notice: 'Appuntamento aggiornato con successo.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @event.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /events/1
  # DELETE /events/1.json
  def destroy
    @event_calendar = EventCalendar.find(params[:event_calendar_id])
    @event.destroy

    respond_to do |format|
      format.html { redirect_to root_url, notice: 'Appuntamento cancellato con successo.'}
      format.json { head :no_content }
    end
  end
end

Answer 1

According to David suggestion I would create a virtual attribute start_at_hours then instead of putting the line inside the controller just edit the Model Event defining a before_update callback as:

# inside your model
before_update :set_hour

def start_at_hours
  if !self.start_at.blank?
    self.start_at.hour
  end
end

def start_at_hours=(value)
end

# model code ...
private
def set_hour
  self.start_at = Time.parse(self.start_at.to_s) + self.start_at_hours.to_i.hours
end

This should work as you need without exceptions.
It’s doing the same thing as David explanation, but directly in the model without the need to change your controller.

Edit: by defining a getter and a setter you can also set the default value for your select (the setter is not needed in this case, but I put it anyway).