mongoose 怎么多个model查询

不如有个A model: aModel = { user_id: String, file_name: String, page_id: Number } B model： fileSchema = new Schema({ page_id: Number, key: String, doc: String, title: String, sym: String });

bModel = { user_id: String, file_name: String, origin_file: String, new_file: [fileSchema] }

已知user_id,file_name,page_id, model find是异步的，怎么同时查找这两个model，得到两个结果后再进行下一步