php+ajax 菜单二级联动

页面：

调研品牌：<select name="brand" id="brand">
    <option value="0" id="b">请选择品牌</option>
    @foreach($oBrands as $oBrand)
        <option value="{{ $oBrand->id }}" id="b">{{ $oBrand->name }}</option>
    @endforeach
</select>
<p></p>
会议主题：<select id="theme" id="theme">
    <option value="0" id="t">请选择主题</option>
</select>

通过ajax级联：

{{--品牌主题级联显示--}}
$(function(){
    $("#brand").change(function(){
        var objectModel = {};
        var   value = $(this).val();
        var   type = $(this).attr('id');
        objectModel[type] =value;
        objectModel['_token'] ='{{ csrf_token() }}';
        $.ajax({
            url:'{{ route("theme") }}', //你的路由地址
            type:"post",
            dataType:"json",
            data:objectModel,
            timeout:30000,
            success:function(data){
                $("#theme").empty();
                var count = data.length;
                var i = 0;
                var b="";
                for(i=0;i<count;i++){
                    b+="<option value='"+data[i].id+"'>"+data[i].name+"</option>";
                }
                $("#theme").append(b);

            }
        });
    });
})

php:

/*
 * 根据品牌级联显示主题
 * */
public function Themes(){
    $brands = $_POST['brand'];
    $oThemes = BrandsAndThemes::where('parent_id','>','0')->where('parent_id',$brands)->get();
    echo json_encode($oThemes);
}