#15881: FilteredSelectMultiple does not respect order
--------------------------------------+------------------------------------
     Reporter:  bmihelac              |                    Owner:  nobody
         Type:  Cleanup/optimization  |                   Status:  new
    Component:  contrib.admin         |                  Version:  1.3
     Severity:  Normal                |               Resolution:
     Keywords:  javascript            |             Triage Stage:  Accepted
    Has patch:  0                     |      Needs documentation:  0
  Needs tests:  0                     |  Patch needs improvement:  0
Easy pickings:  0                     |                    UI/UX:  1
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Comment (by Pawamoy):

 It also does not respect the order of the selected choices when the form
 is reloaded.

 I am using a comma-separated-value-list custom field, which stores choices
 id in the form of a string (ex: '12,66,13').
 When retrieved from the database, this field is converted into a list
 using the split method. The example above would be converted to [12, 66,
 13].

 The first time you create the object with a new form, you can select
 choices one by one, and their order is kept in the resulting list (because
 they are added one by one in the widget right/bottom part by the
 javascript function). But when you save it and reload the page, the order
 is no longer maintained since it is lost while rendering the HTML. The
 selected part is now ordered the same way the available choices are.
 Indeed the javascript code just iterate over the "options" of the
 available part and add them in the chosen part if it encounters the
 "selected" attribute.

 The simplest solution I could think of to solve this is to add another
 attribute or class to the HTML "option" elements with the index of the
 selected choice as value, and use this new value in the javascript code to
 move them in the chosen part according to it.

 == Workaround ==

 === Python code in django.contrib.admin.widgets.Select.render_option ===

 {{{
 if option_value in selected_choices:
     selected_html = mark_safe(' selected="selected" order="%s"' % \
         selected_choices.index(option_value))
 }}}

 This would also require to have a list instead of a set (in
 render_options), because set are unordered:

 {{{
 # selected_choices = set(force_text(v) for v in selected_choices)
 selected_choices = list(force_text(v) for v in selected_choices)
 # Is set used to remove duplicates? If yes then
 # we need more code to remove them from the list too
 }}}

 === Generated HTML ===

 {{{
 <select multiple="multiple" class="filtered" id="id_example_from"
 name="example_old">
   <option title="Choice 1" value="75">Choice 1</option>
   <option title="Choice 2" value="73">Choice 2</option>
   <option title="Choice 3" value="66" selected="selected" order="1">Choice
 3</option>
   <option title="Choice 4" value="13" selected="selected" order="2">Choice
 4</option>
   <option title="Choice 5" value="54">Choice 5</option>
   <option title="Choice 6" value="12" selected="selected" order="0">Choice
 6</option>
 </select>
 }}}

 === JavaScript code in SelectBox.js ===

 {{{
 move: function(from, to) {
     var from_box = document.getElementById(from);
     var to_box = document.getElementById(to);
     var option;
     var ordered_options = [];
     for (var i = 0; (option = from_box.options[i]); i++) {
         if (option.selected && SelectBox.cache_contains(from,
 option.value)) {
             ordered_options.push(option);
         }
     }

     ordered_options.sort(function(a, b) { return a.order - b.order; })

     for (var i = 0; i < ordered_options.length; i++) {
         SelectBox.add_to_cache(to, {
             value: ordered_options[i].value,
             text: ordered_ options[i].text, displayed: 1
         });
         SelectBox.delete_from_cache(from, ordered_options[i].value);
     }
     SelectBox.redisplay(from);
     SelectBox.redisplay(to);
 },
 }}}

 This is just a proposition, I didn't test it yet, but I'll post some
 results when I do.

--
Ticket URL: <https://code.djangoproject.com/ticket/15881#comment:3>
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