Select2 Ajax Method Not Selecting

After looking at another answer it would seem I need to also pass id field with every call, otherwise it will disable the input.

Sample code that fixed it:

$('.select2').select2({
  placeholder: "Policy Name",
  minimumInputLength: 3,
  multiple: false,
  quietMillis: 100,
  id: function(bond){ return bond._id; },
  ajax: {
    url: "http://localhost:3000/search",
    dataType: 'json',
    type: 'POST',
    data: function(term, page) {
      return {
        search: term,
        page: page || 1
      }
    },
    results: function(bond, page) {
      return {results: bond.results, more: (bond.results && bond.results.length == 10 ? true: false)}
    }
  },
  formatResult: formatResult,
  formatSelection: formatSelection,
  initSelection: initSelection
})

Edit

Since this keeps getting upvoted I'll elaborate a bit. The .select2() method expects a unique id field on all results. Thankfully, there's a workaround. The id option accepts a function like this:

function( <INDIVIDUAL_RESULT> ) {
  // Expects you to return a unique identifier.
  // Ideally this should be from the results of the $.ajax() call. 
}

Since my unique identifier was <RESULT>._id, I simply return <RESULT>._id;

Also be careful with the case. I was using Id but select2 expects id. Could save someone's time.

Like Dropped.on.Caprica said: Every result item needs an unique id.

So just assign every result id an unique number:

$('#searchDriver').select2({
    ajax: {
       dataType: 'json',
       delay: 250,
       cache: true,
       url: '/users/search',
       processResults: function (data, params) {
           //data is an array of results
           data.forEach(function (d, i) {
               //Just assign a unique number or your own unique id
               d.id = i; // or e.id = e.userId;
           })

           return {
               results: data
           };
       },
    },
    escapeMarkup: function (markup) { return markup; },
    minimumInputLength: 1,
    templateResult: formatRepo,
    templateSelection: formatRepoSelection
});

The thing is that the JSON data need a property called "id". There's no need for

id: function(bond){ return bond._id; }

If the data does not have an id for itself, you can add it with a function on processResults like here.

        $(YOUR FIELD).select2({
            placeholder: "Start typing...",
            ajax: {
                type: "POST",
                contentType: "application/json; charset=utf-8",
                url: "YOUR API ENDPOINT",
                dataType: 'json',
                data: 
                    function (params) {
                        return JSON.stringify({ username: params.term });
                },
                processResults: function (data, page) {

                    var results = [];

                    $.each(JSON.parse(data.d), function (i, v) {
                        var o = {};
                        o.id = v.key;
                        o.name = v.displayName;
                        o.value = v.key;
                        results.push(o);
                    })

                    return {
                        results: results
                    };
                },
                cache: true
            },
            escapeMarkup: function (markup) { return markup;},
            minimumInputLength: 1,
            templateResult: function (people) {
                if (people.loading)
                    return people.text;

                var markup = '<option value="' + people.value + '">' + people.name + '</option>';

                return markup;
            },
            templateSelection: function (people) { return people.value || people.text }

        });