module ActiveRecord module ConnectionAdapters module MySQL class ExplainPrettyPrinter # :nodoc: # Pretty prints the result of an EXPLAIN in a way that resembles the output of the # MySQL shell: # # +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+ # | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | # +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+ # | 1 | SIMPLE | users | const | PRIMARY | PRIMARY | 4 | const | 1 | | # | 1 | SIMPLE | posts | ALL | NULL | NULL | NULL | NULL | 1 | Using where | # +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+ # 2 rows in set (0.00 sec) # # This is an exercise in Ruby hyperrealism :). def pp(result, elapsed) widths = compute_column_widths(result) separator = build_separator(widths) pp = [] pp << separator pp << build_cells(result.columns, widths) pp << separator result.rows.each do |row| pp << build_cells(row, widths) end pp << separator pp << build_footer(result.rows.length, elapsed) pp.join("\n") + "\n" end private def compute_column_widths(result) [].tap do |widths| result.columns.each_with_index do |column, i| cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s} widths << cells_in_column.map(&:length).max end end end def build_separator(widths) padding = 1 '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+' end def build_cells(items, widths) cells = [] items.each_with_index do |item, i| item = 'NULL' if item.nil? justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust' cells << item.to_s.send(justifier, widths[i]) end '| ' + cells.join(' | ') + ' |' end def build_footer(nrows, elapsed) rows_label = nrows == 1 ? 'row' : 'rows' "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed end end end end end