gistfile1.rb

module GeneratePdf                                                                                                             
  class UserLog                                                                                                                
    def self.pdf(data)                                                                                                         
      disp_fields = DisplayField.find_all_by_report_id(yield.id).map do |field|                                                
        { :field_name => field.field_name , :field_label => field.field_label.capitalize }                                     
      end                                                                                                                      
                                                                                                                               
      list_field_names = disp_fields.collect{ |names| names[:field_name] }                                                     
      list_field_labels = disp_fields.collect{ |label| label[:field_label] }                                                   
                                                                                                                               
      list_field_labels.empty? ? table_width = 0 : table_width = 550                                                           
                                                                                                                               
      Prawn::Document.new do |pdf|                                                                                             
        pdf.text "#{ yield.name } Report", :align => :left                                                                     
        pdf.move_up 10                                                                                                         
        pdf.text Time.now.strftime("%m/%d/%y"),:align => :right                                                                
        pdf.stroke_horizontal_rule                                                                                             
        pdf.move_down 10                                                                                                       
                                                                                                                               
        unless list_field_names.empty? || list_field_labels.empty?                                                             
          pdf.table([list_field_labels],                                                                                       
                    :width => table_width,                                                                                     
                    :cell_style => {:size => 8, :borders => [], :padding => 2 , :align => :left}) do                           
            row(0).style( :background_color => 'dddddd', :size => 8, :font_style => :bold)                                     
          end                                                                                                                  
                                                                                                                               
          data.each do |patient|                                                                                               
            pdf.table([                                                                                                        
                       list_field_names.collect do |field_value|                                                               
                         if patient.send(field_value).class.eql?(Date)                                                         
                           patient.send(field_value).strftime("%m/%d/%Y")                                            
                         else                                                                                                  
                           patient.send(field_value)                                                      
                         end                                                                                                   
                       end                                                                                                     
                      ],:width => table_width, :cell_style => {:size => 8, :borders => [], :padding => 2 , :align => :left})   
          end                                                                                                                  
        end                                                                                                                    
      end.render                                                                                                               
    end                                                                                                                        
  end                                                                                                                          
end 

a pdf generation code for code in my app