小编pyf*_*l88的帖子

| id    | user_id | created_at (datetime) |
| 1     | 1       | 17 May 2016 10:31:34  |
| 2     | 1       | 17 May 2016 12:41:54  |
| 3     | 2       | 18 May 2016 01:13:57  |
| 4     | 1       | 19 May 2016 07:21:24  |
| 5     | 2       | 20 May 2016 11:23:21  |
| 6     | 1       | 21 May 2016 03:41:29  |

如何获得唯一且最新的created_at user_id记录的结果,在上述情况下将是记录ID 5和6？

到目前为止我尝试过的

到目前为止,我试图使用group_by返回这样的哈希:

Table.all.group_by(&:user_id)

#{1 => [record 1, record 2, …

我有一个在webpack js中呈现的日历模块- app/javascript/packs/application.js

document.addEventListener('DOMContentLoaded', function() {
  var calendarEl = document.getElementById('calendar');

  var calendar = new Calendar(calendarEl, {
    plugins: [ interactionPlugin, dayGridPlugin, timeGridPlugin, listPlugin, momentPlugin ],
    header: {
      left: 'prev,next today',
      center: 'title',
      right: 'dayGridMonth,timeGridWeek,timeGridDay,listWeek'
    },
    defaultDate: '2018-01-12',
    navLinks: true, // can click day/week names to navigate views
    editable: true,
    eventLimit: true, // allow "more" link when too many events
    selectable: true,
    events: '/events.json',
    select: function(info) {
      $.getScript('/events/new', function(){
        $('#event_date_range').val(moment(info.start).format('YYYY-MM-DD HH:mm') + ' - ' + moment(info.end).format('YYYY-MM-DD HH:mm'));
        $('#start_date').val(moment(info.start).format('YYYY-MM-DD HH:mm'));
        $('#end_date').val(moment(info.end).format('YYYY-MM-DD HH:mm')); …

我使用 nokogiri 将 xml 文档解析为哈希数组：

助手/国家.helper

module CountriesHelper

  def parse
    @countries = ['australia', 'canada', 'france']
    @countries.inject([]) do |memo, country|
    File.open("public/#{country}.xml") do |f|
    xml = Nokogiri::XML(f)
    path = "//country/stores/"
      memo << xml.xpath(path).map do |x|
           { 'country' => x.parent['country'],
           'store' => x['store']}
    end
   end
  end

# [{"country"=>"australia", "store"=>"store1"}, {"country"=>"france", "store"=>"store2"}]

如何将这个哈希格式数组保存到我的数据库中？假设我有两个模型 Country 和 Store。

我有这个数组:

a = [[1,2,3,4,5],[3,5,6,8,12,45],[3,2,1,5,7,9,10,11],[3,5,6,8,2,1,3,4,6]]

我想合并它的内部数组,使它们成为:

a = [[1,2,3,4,5,3,5,6,8,12,45],[3,2,1,5,7,9,10,11,3,5,6,8,2,1,3,4,6]]

我怎样才能做到这一点？