controller_timesheets.rb

# /app/controllers/timesheets_controller.rb
class TimesheetsController < ApplicationController
  has_scope :by_employee
  has_scope :by_place    
  def index
    @timesheets = apply_scopes(Timesheet).all
  end
end

exec.txt

http://localhost:3000/timesheets?by_employee=1&by_place=3

model_timesheet.rb

# /app/models/timesheet.rb
class Timesheet < ActiveRecord::Base
  named_scope :by_employee, proc { |employee| { :conditions => { :employee_id => employee } } }
  named_scope :by_place, proc { |place| { :conditions => { :place_id => place } } }
end

view_timesheets_filter.erb

  # /app/views/timesheets/_filter.html.erb
<% form_tag ('/timesheets', :method => :get) do -%>
  <%= select_tag 'by_employee', options_for_select(@employees, params[:by_employee].to_i) %>
  <%= select_tag 'by_place', options_for_select(@places, params[:by_place].to_i) %>
  <%= content_tag(:button, "Search", :type => "submit") %>
<% end -%>