ajax_filtered_fields = {
   
    request_url: "/ajax_filtered_fields/json_index/",
    data_loaded: "data_loaded",
   
    _appendOption: function(obj, selector) {
        // append a json data row as an option to the selector
        var option = $('<option>' + obj[1] + '</option>');
        option.attr({value: obj[0]});
        option.appendTo(selector);
        return option;
    },
   
    _removeOptions: function(selector) {
        // remove all options from selector
        selector.children("option").each(function(i) {
           $(this).remove();
        });
    },
       
    getManyToManyJSON: function(element_id, app_label, object_name, lookup_string, select_related) {
        // manage the ManyToMany ajax request
        var selector_from = $("#" + element_id + "_from");
        var selector_to = $("#" + element_id + "_to");
       
        $("#" + element_id + "_input").val("");
        selector_from.attr("disabled", true);
        selector_to.attr("disabled", true);

        this._removeOptions(selector_from);
       
        $.getJSON(this.request_url, {
            app_label: app_label,
            object_name: object_name,
            lookup_string: lookup_string,
            select_related: select_related},
            function(data){
                $.each(data, function(i, obj){
                    var option_is_selected = selector_to.children("option[value='" + obj[0] + "']").length;
                    if (!option_is_selected) {
                        ajax_filtered_fields._appendOption(obj, selector_from);
                    };
                });
                SelectBox.init(element_id + "_from");
                selector_from.attr("disabled", false);
                selector_to.attr("disabled", false);
                selector_from.trigger(ajax_filtered_fields.data_loaded);
            });
    },
   
    getForeignKeyJSON: function(element_id, app_label, object_name, lookup_string, select_related) {
        // manage the ForeignKey ajax request
        var selector = $("#" + element_id);
        var hidden = $("#hidden-" + element_id);

        $("#" + element_id + "_input").val("");
        selector.attr("disabled", true);
       
        this._removeOptions(selector);
       
        $.getJSON(this.request_url, {
            app_label: app_label,
            object_name: object_name,
            lookup_string: lookup_string,
            select_related: select_related},
            function(data){
                var selection = hidden.val();
                ajax_filtered_fields._appendOption(new Array("", "---------"), selector);
                $.each(data, function(i, obj){
                    ajax_filtered_fields._appendOption(obj, selector);
                });
                selector.children("option[value='" + selection + "']").attr("selected", "selected");
                selector.attr("disabled", false);
                SelectBox.init(element_id);
                ajax_filtered_fields.bindForeignKeyOptions(element_id);
                selector.trigger(ajax_filtered_fields.data_loaded);
            });
    },
   
    bindForeignKeyOptions: function(element_id) {
        // bind the dummy options to the hidden field that do the work
        var selector = $("#" + element_id);
        var hidden = $("#hidden-" + element_id);
        selector.change(function(e) {
            hidden.val($(this).val());
        });
    }
           
};