reimplement_dynamic_finders

my_dynamic_finders.rb

module MyDynamicFinders
  private

  def method_missing(symbol, *arg, &block)
    if symbol.to_s.start_with?('find_by_')
      sym_str = symbol.to_s.end_with?('!') ? symbol.to_s.chop : symbol.to_s
      conds = sym_str.gsub!(/find_by_/, '').split('_and_').zip(arg)
      ret = $DATABASE.find do |user|
        conds.inject(true) do |acc, cond|
          acc && ( user.public_send("#{cond[0]}".to_sym) == cond[1] )
        end
      end
      symbol.to_s.end_with?('!') ? ( ret || raise ) : ret
    else
      super
    end
  end

  def respond_to_missing?(symbol, *arg)
    if symbol.to_s.start_with?('find_by_')
      true
    else
      super
    end
  end
end

改善版

module MyDynamicFinders
  private

  def method_missing(symbol, *arg, &block)
    if symbol.to_s.start_with?('find_by_')
      sym_str = symbol.to_s.end_with?('!') ? symbol.to_s.chop : symbol.to_s
      conds = sym_str.gsub!(/find_by_/, '').split('_and_').zip(arg)
      ret = $DATABASE.find do |user|
        conds.all? do |attr, value|
          user.public_send("#{attr}".to_sym) == value
        end
      end
      symbol.to_s.end_with?('!') ? ( ret || raise ) : ret
    else
      super
    end
  end

  def respond_to_missing?(symbol, *arg)
    if symbol.to_s.start_with?('find_by_')
      true
    else
      super
    end
  end
end