dbdocs.rb

require 'sinatra'
require 'active_record'

ActiveRecord::Base.establish_connection(
  :adapter => 'mysql',
  :encoding => 'utf8',
  :database => 'foo',
  :username => 'bar',
  :password => 'baz',
  :host => 'localhost'
)

class Table
  attr_accessor :name
  
  def columns
    ActiveRecord::Base.connection.execute("show fields from #{@name};")
  end
end

def yes_no_to_null(x)
  case x
  when "YES"
    "NULL"
  when "NO"
    "NOT NULL"
  end
end

get '/' do
  @tables = Array.new 
  ActiveRecord::Base.connection.execute('show tables;').each do |t| 
    table = Table.new
    table.name = t[0] 
    @tables << table
  end
  
  erb :index
end  

__END__

@@ index
<% @tables.each do |table| %>
  <h3><u><%= table.name %></u></h3>
  <% table.columns.each do |column| %>
    <p>-<strong><%= column[0] %></strong> <i><%= column[1] %></i> <%= yes_no_to_null(column[2]) %></p>  
  <% end %>
  <br />  
<% end %>