title: When a list of categories becomes available in store A, select one category and set its ID in store B
body: <p>I have two stores - GroupsStore and ItemsFilterStore. The ItemsFilterStore's state should contain a choice of a single Group from the groups available in the GroupsStore, but:</p>
  
  <ul>
  <li><p>the groups are not initially available in the GroupsStore, so the choice in the ItemsFilterStore cannot initially be made (the constructor initializes it to null).</p></li>
  <li><p>once the groups become available in the GroupStore, I need to perform an action that will select one group (according to some logic) and set its ID in the ItemsFilterStore.</p></li>
  </ul>
  
  <p><strong>THE PROBLEM:</strong></p>
  
  <p>I read <strong>EVERYWHERE</strong> that triggering actions from action handlers in a store is an antipattern.</p>
  
  <p>So how do I engineer this correctly?</p>