laravel ajax post不返回值

Question

我正在尝试在laravel中执行ajax帖子。我有一个控制器“show_freeCars”awich从ajax post获取一些值并执行查询以返回结果。我有这个：

    public function show_freeCars() {
            $starttime = Input::get('starttime');
            $endtime = Input::get('endtime');
            $enddate = Input::get('enddate');
            $startdate = Input::get('startdate');
            $classes = Input::get('classes');

            $free_cars = DB::select('SELECT * FROM cars WHERE id NOT IN (select distinct c.id from cars as c '
                            . 'left join rentals as r on c.id = r.vehicle '
                            . 'where STARTTIME="' . $startdate . ' ' . $starttime . '" '
                            . 'AND ENDTIME="' . $enddate . ' ' . $endtime . '" '
                            . 'AND (r.status="REZERVATION" OR r.status="CHECK_OUT") '
                            . 'order by c.id) AND class= "' . $classes . '" ');
            if (Request::ajax()) {
                $response_values = array(
                    'success' => 1,
                    'values' => $free_cars,
                );
                return Response::json($response_values);
            } else {
                dd('error');


  }
    }

和javascript

jQuery('#form-reservation').submit(function()
    {
        var startdate = $('input[name$="startdate"]').val();
        var starttime = $('input[name$="starttime"]').val();
        var enddate = $('input[name$="enddate"]').val();
        var endtime = $('input[name$="endtime"]').val();
        var classes = $('input[name$="classes"]').val();
        var url = $(this).attr("action");
        jQuery.ajax({
            url: url,
            type: "post",
            data: {
                startdate: startdate,
                starttime: starttime,
                enddate: enddate,
                endtime: endtime,
                classes: classes
            },
            datatype: "json",
            beforeSend: function()
            {
                jQuery('#ajax-loading').show();

            }
        })
                .done(function(data)
                {
                    $('#cars_table').empty()
                    if (data.success === 1)
                    {
                        var arr = data.values;
                        alert(arr);
                    }
                    else {
                        window.location = data.redirect_to;
                    }
                })
                .fail(function(jqXHR, ajaxOptions, thrownError)
                {
                    alert('Invalid Data');
                });
        return false;
    });

警告空。但是，如果我从控制器中删除行$classes = Input::get('classes');和AND class= "' . $classes . '" '，则会显示结果。查询没问题，因为我用dd（$ free_cars）测试了它，它显示了汽车列表。只是有些东西被ajax返回值搞砸了。为什么它返回null？