Multiple Filter via Scope

availability.rb

class Availability < ActiveRecord::Base
  attr_accessible :name, :hospital_tokens, :start_at, :end_at, :shift 
  has_many :appointments
  has_many :hospitals, :through => :appointments
  belongs_to :user
  has_event_calendar
  attr_reader :hospital_tokens
  
  scope :by_hospital, lambda { |hospital| selected_hospital(hospital) }
  scope :by_date, lambda { |date| where("start_at >= ? AND start_at <= ?", date, date) }
  scope :by_specialty, lambda { |specialty| joins(:user => [{:profile => :specialties}]).where("specialty_id = ?", specialty) }
  scope :by_shift,lambda { |shift| where("shift = ?", shift) }
  
  def hospital_tokens=(ids)
    self.hospital_ids = ids.split(",")
  end
  
  private
    def self.selected_hospital(hospital)
      where("hospital_id IN (?)", hospital).joins(:appointments)
    end
end

order.rb

class Order < ActiveRecord::Base
  belongs_to :hospital
  belongs_to :specialty
  validates_presence_of :shift, :hospital, :specialty, :shift_date
  validates_presence_of :created_by, :status, :on => :create
  validates_presence_of :updated_by, :status, :on => :update
end

orders_controller.rb

class OrdersController < ApplicationController
  load_and_authorize_resource
  
  def index
    @orders = Order.all
  end
  
  def create
    params[:order][:shift_date] = Date.strptime(params[:order][:shift_date],'%m/%d/%Y')
    @order = Order.create(params[:order])
    @order.created_by = current_user.profile.full_name
    @order.status = "Open"
    if @order.save
      flash[:notice] = "Order created"
      redirect_to edit_order_path(@order)
    else
      flash[:alert] = "Please fill up required fields"
      render :action => 'new'
    end
  end
  
  def edit
    @order = Order.find(params[:id])
    @available_nurses = Availability.by_hospital(@order.hospital)
                                    .by_date(@order.shift_date)
                                    .by_shift(@order.shift)
                                    .by_specialty(@order.specialty_id)
  end
  
end