model_format.rb

module ModelFormat
  
  #fields = [
  #  ["column1", :method1],
  #  ["column2", :method2],
  #  ["column3", [:method3_1, :method3_2]],
  #]
  def define_csv(fields)
    define_method :to_csv do
      headers, columns = fields.transpose
      
      records = all.map do |obj|
        columns.map do |col|
          methods = [col] unless col.instance_of?(Array)
          methods.reduce(obj) {|o, m| o.send m }
        end
      end
      
      rows = [headers] + records
      
      CSV.generate(col_sep: "\t") do |csv|
        rows.each do |row|
          csv << row if row
        end
      end
      
    end
  end
  
end