select2: How to display pre-filled options properly to the user?

Question

I have a working select2 implementation on this jsfiddle . It enables a search for Github repo's and returns the results so they can be selected by the user. If only 1 repo matches a given search it will be auto-selected.

I need to be able to pre-fill my select2 form with some default options. As stated in the docs I should be able to do something like this:

<select id='select2_element' multiple='multiple' style='width:100%;'>
  <option value="easypr-ja" selected="selected">EasyPR-Java 70 32393764</option>
</select>

When I press the console.log all selected data button I can see that the id and text of my pre-filled repo is accessible, but in the browser, the above pre-filled option gets displayed as undefined undefined easypr-ja .

What do I need to do in order to get the value of the default option displayed properly?

My implementation is doing some custom formatting as shown here:

var createRepo, formatRepo, formatRepoSelection, selectRepos;

formatRepoSelection = function(element) {
  return element.name + ' ' + element.forks + ' ' + element.id;
};

formatRepo = function(element) {
  var markup;
  if (!element.loading) {
    return markup = element.name + ' ' + element.id;
  }
};

createRepo = function() {
  $(".btn-create-repos").off("click");
  return $(".btn-create-repos").click(function(e) {
    var el, element_ids;
    el = $(e.currentTarget);
    element_ids = $("#select2_element").select2('data');
    return console.log(element_ids);
  });
};

selectRepos = function() {
  var option, select2_element;
  select2_element = $('#select2_element');
  select2_element.select2({
    placeholder: "Type in 'easypr-ja' to get only 1 result",
    ajax: {
      url: "https://api.github.com/search/repositories",
      dataType: 'json',
      delay: 250,
      data: function (params) {
        return {
          q: params.term,
          page: params.page
        };
      },
      processResults: function (data, params) {

        if (data.items.length === 1) {
          setTimeout(function() {
              $("#select2-select2_element-results li:first-child").trigger('mouseup');
          }, 0);
          return {
            results: data.items
          };
        } else {
          params.page = params.page || 1;

          return {
            results: data.items,
            pagination: {
              more: (params.page * 30) < data.total_count
            }
          };
        }
      },
      cache: true
    },

    escapeMarkup: function(markup) {
      return markup;
    },
    minimumInputLength: 2,
    templateResult: formatRepo,
    templateSelection: formatRepoSelection
  });
};

$(function() {
  selectRepos();
  return createRepo();
});

Answer 1

Please follow below example with form_for, It may be helpful

<%= f.select(:categories, Category.all.collect {|c| [c.name, c.id]}, {}, id: "event_categories", :multiple => true) %>

<script type="text/javascript">
    $("#event_categories").select2();
    <% if @event.id.present?%>
        $("#event_categories").val(<%= @event.categories.collect(&:id)%>).change()
    <% elsif params[:action]=="create" || params[:action]=="update" %>
        $("#event_categories").val(<%=params[:event][:categories].map(&:to_i).drop(1)%>).change()
    <% end %>
</script>