How to pre-select values in select2 multi select?

Question

I am having a multiple select like this:

<select multiple="multiple" class="myList">
        <option value="1" selected="selected">Apple</option>
        <option value="2" selected="selected">Mango</option>
        <option value="3" selected="selected">Orange</option>
</select>

Now, apart from those options which must come selected in the select box, I wanted additional ajax functionality which would give values from a remote source.

Here is my code for select2

$(function(){
    $(".myList").each(function(){

                $(this).select2({
                placeholder: "Search for fruits",
                minimumInputLength: 2,
                multiple: true,
                id: function(e) { 
                return e.id+":"+e.name; },
                ajax: {
                    url: "https://localhost:8443/fruit_search",
                    dataType: 'json',
                    data: function(term, page) {
                        return {
                            q: term
                        };
                    },
                    results: function(data, page) {
                    var frts=[];
                        $.each(data,function(idx,Frt){
                            frts[frts.length]=Frt;
                        });
                        return {
                            results: frts
                        };
                    }
                },
                initSelection: function(element, callback) {
                    var data = [];
                },
                formatResult: formatResult,
                formatSelection: formatSelection
                });
        });

});

But I am getting the error:

Error: Option 'id' is not allowed for Select2 when attached to a <select> element.

But when I use <input type="hidden"> then where should I keep the pre-selected options? How do I show them up when the select2 box appears?

Answer 1

If you only have values then you can use 'val' to get pre-selected values like this.

var PRESELECTED_FRUITS = [ '1','2','3'];

$('.myList').select2({}).select2('val', PRESELECTED_FRUITS);  

Answer 2

You can use the "data" function to set the initial values:

var PRESELECTED_FRUITS = [
    { id: '1', text: 'Apple' },
    { id: '2', text: 'Mango' },
    { id: '3', text: 'Orange' }
];

$('.myList').select2('data', PRESELECTED_FRUITS)

Note: The "val" function is another way to set the initial values, but you only specify the ids with that function. In that case you would have to supply an "initSelection" function that builds the objects from the ids.

Also note that the "id" option is not the only option that is forcing you to use a hidden input. You cannot use the "ajax" option with a select element either.

As for the "id" option, I don't think you need it. Just put logic in the ajax "results" function so it builds an array of objects that have the proper id and text properties, or have the server return objects with those properties.

jsfiddle demo