ruby-on-rails - Rails_Admin 相关的下拉菜单

Question

有没有办法根据另一个下拉列表的值过滤下拉列表？
例如，如果我们有: Class 和 Student 模型，其中 Student 有 class_id；有没有办法根据所选的 Class 过滤下拉列表中显示的学生？

EDIT

显然，rails_admin gem 具有我正在寻找的 association 关系；但它并不完美。

Answer 1

给定两个 <select>元素 "Class"和 "Student" , 与 Student列表包含 data-class_id属性引用来自 Class 的值列表(见下面的片段)，你可以过滤 "Student"基于 "Class" 的下拉列表使用以下 vanilla-JavaScript 代码的下拉列表的值:

var firstSelectId = "Class";
var secondSelectId = "Student";
var data_attr = "class_id";
this.addEventListener("DOMContentLoaded", function(event) {
  var firstSelect = document.getElementById(firstSelectId);
  var secondSelect = document.getElementById(secondSelectId);
  firstSelect.addEventListener("change", function(event) {
    var value = event.target.value;
    Array.prototype.forEach.call(secondSelect.options, function(item) {
      item.style.display = (item.dataset[data_attr] === value) ? 'inline' : 'none';
    });
    var selected = secondSelect.selectedOptions[0];
    if (selected && selected.dataset[data_attr] !== event.target.value) {
      secondSelect.selectedIndex = -1;
    }
  });
  firstSelect.dispatchEvent(new Event('change'));
});

<form id="myform">
  Select a class and student:
  <select id="Class">
    <option value="1">Class1</option>
    <option value="2">Class2</option>
    <option value="3">Class3</option>
  </select>
  <select id="Student">
    <option value="StudentA" data-class_id="1">A</option>
    <option value="StudentB" data-class_id="2">B</option>
    <option value="StudentC" data-class_id="3">C</option>
    <option value="StudentD" data-class_id="2">D</option>
    <option value="StudentE" data-class_id="1">E</option>
    <option value="StudentF" data-class_id="1">F</option>
  </select>
</form>