module MysqlCompat

def self.define_all_hashes_method!
  raise 'Mysql not loaded' unless defined?(::Mysql)
  target = defined?(Mysql::Result) ? Mysql::Result : MysqlRes
  return if target.instance_methods.include?('all_hashes') ||
            target.instance_methods.include?(:all_hashes)
  # Ruby driver has a version string and returns null values in each_hash
  # C driver >= 2.7 returns null values in each_hash
  if Mysql.const_defined?(:VERSION) && (Mysql::VERSION.is_a?(String) || Mysql::VERSION >= 20700)
    target.class_eval <<-'end_eval'
    def all_hashes                     # def all_hashes
      rows = []                        #   rows = []
      each_hash { |row| rows << row }  #   each_hash { |row| rows << row }
      rows                             #   rows
    end                                # end
    end_eval
  # adapters before 2.7 don't have a version constant
  # and don't return null values in each_hash
  else
    target.class_eval <<-'end_eval'
    def all_hashes                                            # def all_hashes
      rows = []                                               #   rows = []
      all_fields = fetch_fields.inject({}) { |fields, f|      #   all_fields = fetch_fields.inject({}) { |fields, f|
        fields[f.name] = nil; fields                          #     fields[f.name] = nil; fields
      }                                                       #   }
      each_hash { |row| rows << all_fields.dup.update(row) }  #   each_hash { |row| rows << all_fields.dup.update(row) }
      rows                                                    #   rows
    end                                                       # end
    end_eval
  end
  unless target.instance_methods.include?('all_hashes') ||
         target.instance_methods.include?(:all_hashes)
    raise "Failed to defined #{target.name}#all_hashes method. Mysql::VERSION = #{Mysql::VERSION.inspect}"
  end
end