javascript - 如何正确解决此 knex.js promise ？

Question

我正在使用 knex，这是我在从数据库请求后获取 Question_info 对象的代码。

let question_info = knex.select('id', 'question', 'pre_question', 'response_options_id').from('_questions').whereNot({'progress': 100}).andWhere({'school_id': school_id}).orderBy('date_created', 'asc')
        .map((question) => {
            //going through all possible questions
            helpers.debug("Question", question);
            //checking if there are responses
            return knex('_responses').where({'question_id': question.id, 'student_id': event.user.id}).first()
                .then((response) => {
                    //if no responses, return question_info object
                    if(!response){
                        return knex.select('options_json').from('_response_options').where({'id': question.response_options_id}).first()
                            .then((options) => {
                                return {
                                    question_id: question.id,
                                    question: question.question,
                                    pre_question: question.pre_question,
                                    response_options: JSON.parse(options.options_json)
                                }
                            });
                    }
                });     
        }).catch((e) => {
            console.error('Error', e);
        });

当第一个问题已经得到解答时，我的返回值显示为空。如何正确使用 knex 获得不带 null 的返回数组。

[
  null,
  {
    "question_id": "2",
    "question": "What is second question?",
    "pre_question": "Hey!!",
    "response_options": [
      {
        "title": "Yes",
        "value": "Yes"
      },
      {
        "title": "Maybe",
        "value": "Maybe"
      },
      {
        "title": "No",
        "value": "No"
      }
    ]
  },
  {
    "question_id": "3",
    "question": "Third Question?",
    "pre_question": "Yo",
    "response_options": [
      {
        "title": "Yes",
        "value": "Yes"
      },
      {
        "title": "Maybe",
        "value": "Maybe"
      },
      {
        "title": "No",
        "value": "No"
      }
    ]
  }
]

Answer 1

看起来您的问题是，如果第二个查询确实返回了响应，那么您不会返回任何内容。

// this part of your code seems to be wrong
if (!response) {
  // return choices because there was no response found
  return knex('choices')...
}

应该是这样的:

// this part of your code seems to be wrong
if (!response) {
  // return choices because there was no response found
  return knex('choices')...
} else {
  return response;
}

编辑这或多或少是如何使用单个查询和连接做同样的事情(我没有测试这个，所以它可能不起作用，但它应该给出如何实现它的一般概念):

let question_info = knex('_questions as q')
  .select(
     'id', 
     'question', 
     'pre_question', 
     'response_options_id',
     'r.id as r_id',
     'options_json'
  )
  .join('_responses as r', builder => {
    builder
      .on('q.id', 'r.question_id')
      .onVal('r.student_id', event.user.id);
  })
  .join('_response_options as ro', 'q.response_options_id', 'ro.id')
  .where('q.school_id', school_id)
  .whereNot('q.progress', 100)
  .whereNull('r.id')
  .orderBy('q.date_created', 'asc')
  .map(notAnsweredQuestion => {
    return {
      question_id: notAnsweredQuestion.id,
      question: notAnsweredQuestion.question,
      pre_question: notAnsweredQuestion.pre_question,
      response_options: JSON.parse(notAnsweredQuestion.options_json)
    };
  }).catch((e) => {
    console.error('Error', e);
  });