Select2 & rails

search_controller.rb

class SearchController < ApplicationController
  respond_to :json
  def index
    render json: @your_results, each_serializer: YourSerializer , root: :results
  end
end

select_binder.js

//using lodash (https://lodash.com/docs)
$(document).ready(function(){
  $("#search_event").select2({
    placeholder: "Search for a object by name",
    minimumInputLength: 3,
    dataType: 'json',
    minimumResultsForSearch: Infinity,    
    id: function(result){ return result.id;},
      ajax: {
          url: "/en/search",
          data: function (term, page) {          
              return {
                  query: term
              };
          },
          processResults: function(data, page) {
            //do this if your ajax response is not in the format {id: 'element id', text: 'text' }
            var results = [];
            _.each(data.results, function(result){
              results.push({
                id: result.id,
                text: result.name
                //do this if your ajax response is not in the format {id: 'element id', text: 'text' }
              });
            })
            return {
              results: results
            }
          },
        cache: true
      },
      formatResult: eventResult,    
      formatSelection: eventSelection,
      //escapeMarkup: function (m) { return m; }    
  });

  function eventResult(result) {
      return result.name;
      //return "<img src=" + event.event.picture + "></>";
  }

  function eventSelection(event) {  
      return result.name;
  }
});

//sorry about the indentation. bad copy/paste. I'll improve later hopefully :-)