to_spreadsheet is a gem that lets you render xls from your existing haml/erb views from Rails (>= 3.0).

Installation

Add it to your Gemfile:

gem 'to_spreadsheet'

Usage

In your controller:

# my_thingies_controller.rb
class MyThingiesController < ApplicationController
  respond_to :xls, :html
  def index
    @my_items = MyItem.all
    respond_to do |format|
      format.html 
      format.xlsx { render xlsx: :index, filename: "my_items_doc" }
    end
  end
end

In your view partial:

# _my_items.haml
%table
  %caption My items
  %thead
    %tr
      %td ID
      %td Name
  %tbody
    - my_items.each do |my_item|
      %tr
        %td.number= my_item.id
        %td= my_item.name
  %tfoot
    %tr
      %td(colspan="2") #{my_items.length}

In your index.xls.haml:

# index.xls.haml
= render 'my_items', my_items: @my_items

In your index.html.haml:

# index.html.haml
= link_to 'Download spreadsheet', my_items_url(format: :xlsx)
= render 'my_items', my_items: @my_items

Worksheets

Every table in the view will be converted to a separate sheet.
The sheet title will be assigned to the value of the table’s caption element if it exists.

Formatting

You can define formats in your view file (local to the view) or in the initializer

format_xls 'table.my-table' do
  workbook use_autowidth: true
  sheet    orientation: landscape
  format 'th', b: true # bold
  format 'tbody tr', color: lambda { |row| 'ddffdd' if row.index.odd? }
  format 'A3:B10', i: true # italic
  format column: 0, width: 35
  format 'td.custom', lambda { |cell| modify cell somehow.}
  # default value (fallback value when value is blank or 0 for integer / float)
  default 'td.price', 10

For the full list of supported properties head here: http://rubydoc.info/github/randym/axlsx/Axlsx/Cell
In addition, for column formats, Axlsx columnInfo properties are also supported

Themes

You can define “themes” – blocks of formatting code:

ToSpreadsheet.theme :zebra do
  format 'tr', color: lambda { |row| 'ddffdd' if row.index.odd? }

And then use them:

format_xls 'table.zebra', ToSpreadsheet.theme(:zebra)

Types

The default theme uses class names on td/th to cast values.
Here is the list of class to type mapping:

CSS class	Format
decimal or float	Decimal
num or int	Integer
datetime	DateTime (Chronic.parse)
date	Date (Date.parse)
time	Time (Chronic.parse)