base_report.rb

class BaseReport
  # encapsulate common functionality for gathering report parameters
    
  def initialize(attrs={})
    date_time_attributes = {}
    
    # this is a naive implementation of recognizing rails' multipart parameters (eg for datetime selects)
    # we are assuming either date / datetime, and discarding any datatype component
    attrs.each do |k,v|
      if k.to_s.include?("(")
        # assume this is a date/time parameter : extract parts to build entire value
        attribute_name, position = k.split("(")
        position = position.to_i
        
        date_time_attributes[attribute_name] ||= []
        date_time_attributes[attribute_name] << [position, v.to_i]
      else
        setter = "#{k}=".to_sym
        self.send(setter, v) if self.respond_to?(setter)
      end
    end
    
    # add date attributes
    date_time_attributes.each do |k, v|
      setter = "#{k}=".to_sym
      if self.respond_to?(setter)
        # extract the actual multipart value in the right order
        args = v.sort.map{|pair| pair[1] }
        case args.length
        when 3
          # assume it's a date
          self.send(setter, Date.new(*args))
        when 6
          # assume it's a datetime
          self.send(setter, Time.new(*args))
        else
        end
      end
    end
  end
end

customers_controller.rb

class Admin::Reports::CustomersController < Admin::Reports::BaseController
  class Report < BaseReport
    attr_accessor :start_date
    attr_accessor :end_date
  end
    
  def index
    @report = Report.new(
      :start_date => 1.month.ago.at_beginning_of_month,
      :end_date => 1.month.ago.at_end_of_month
    )
  end
  
  def execute
    @report = Report.new(params[:report])
    @customers = Customer.find(:all, :conditions => ["created_at BETWEEN ? AND ?", @report.start_date, @report.end_date], :order => "source, created_at")

    respond_to do |format|
      format.html
      format.xls {
        headers['Content-Type']='application/vnd.ms-excel; charset=utf-8'
        headers['Content-Disposition'] = %{attachment; filename="Customers-#{@report.start_date.strftime('%Y%m%d')}-#{@report.end_date.strftime('%Y%m%d')}.xls"}
        headers['Cache-Control'] = ''

        render :layout => false
      }
    end
  end
end

execute.html.erb

<h1>New Customers</h1>

<table>
  <tr>
    <th>Organization Name</th>
    <th>Signup Date</th>
    <th>Revenue</th>
  </tr>
  <%- @customers.each do |customer| -%>
  <tr class="<%= cycle('even_row', 'odd_row') %>">
    <td><%= customer.organization_name %></td>
    <td><%= date_mdy customer.created_at %></td>
    <td align="right"><%= number_to_currency customer.revenue %></td>
  </tr>
  <%- end -%>
</table>

execute.xml.builder

xml.instruct! :xml, :version=>"1.0", :encoding=>"UTF-8"
xml.Workbook({
  'xmlns'      => "urn:schemas-microsoft-com:office:spreadsheet",
  'xmlns:o'    => "urn:schemas-microsoft-com:office:office",
  'xmlns:x'    => "urn:schemas-microsoft-com:office:excel",
  'xmlns:html' => "http://www.w3.org/TR/REC-html40",
  'xmlns:ss'   => "urn:schemas-microsoft-com:office:spreadsheet"
  }) do

  xml.Styles do
    xml.Style 'ss:ID' => 'Default', 'ss:Name' => 'Normal' do
      xml.Alignment 'ss:Vertical' => 'Bottom'
      xml.Borders
      xml.Font 'ss:FontName' => 'Verdana'
      xml.Interior
      xml.NumberFormat
      xml.Protection
    end
    xml.Style 'ss:ID' => 'currency', 'ss:Name' => 'Currency' do
      xml.NumberFormat 'ss:Format' => '_("$"* #,##0.00_);_("$"* \(#,##0.00\);_("$"* "-"??_);_(@_)'
    end
  end

  xml.Worksheet 'ss:Name' => "Customers" do
    xml.Table do
      # Header
      xml.Row do
        xml.Cell do
          xml.Data 'Customer Name', 'ss:Type' => 'String'
        end
        xml.Cell do
          xml.Data 'Signup Date', 'ss:Type' => 'String'
        end
        xml.Cell do
          xml.Data 'Revenue', 'ss:Type' => 'String'
        end
        # OTHER HEADERS AS NEEDED
      end

      @customers.each do |customer|
        xml.Row do
          xml.Cell do
            xml.Data customer.name, 'ss:Type' => 'String'
          end
          xml.Cell do
            xml.Data customer.created_at.to_s, 'ss:Type' => 'String'
          end
          xml.Cell do
            xml.Data @orders[customer.id], 'ss:Type' => 'Number'
          end
          # OTHER CELLS AS NEEDED
        end
      end

    end # xml.Table
  end # xml.Worksheet
end # xml.Workbook

index.html.erb

<h1>New Customers</h1>

<%= start_form_tag(:action => "execute") %>
  <p>
    <label for="report_start_date">Start Date:</label><br/>
    <%= date_select :report, :start_date %>
  </p>
  
  <p>
    <label for="report_end_date">End Date:</label><br/>
    <%= date_select :report, :end_date %>
  </p>
  
  <%= submit_tag "Execute" %>
<%= end_form_tag %>