Question

我正在尝试从func change(a interface{}) { rv := reflect.ValueOf(a) changerv(rv) } func changerv(rv reflect.Value) { if rv.Kind() == reflect.Ptr { rv = rv.Elem() } if rv.Kind() == reflect.Struct { changeStruct(rv) } if rv.Kind() == reflect.Slice { changeSlice(rv) } } // assumes rv is a slice func changeSlice(rv reflect.Value) { ln := rv.Len() if ln == 0 && rv.CanAddr() { var elem reflect.Value typ := rv.Type().Elem() if typ.Kind() == reflect.Ptr { elem = reflect.New(typ.Elem()) } if typ.Kind() == reflect.Struct { elem = reflect.New(typ).Elem() } rv.Set(reflect.Append(rv, elem)) } ln = rv.Len() for i := 0; i < ln; i++ { changerv(rv.Index(i)) } } // assumes rv is a struct func changeStruct(rv reflect.Value) { if !rv.CanAddr() { return } for i := 0; i < rv.NumField(); i++ { field := rv.Field(i) switch field.Kind() { case reflect.String: field.SetString("fred") case reflect.Int: field.SetInt(54) default: fmt.Println("unknown field") } } }保存数组中的数据，但是每次我得到空数组时，我都不明白它是范围内的还是方法db.get(...) => {...}？请帮我解决这个问题。我的主要目标

db.get(...) => {...}

我想做的是获取const sqlite3 = require('sqlite3'); let db = new sqlite3.Database('./ProblemsForPatan.db', sqlite3.OPEN_READONLY); let sql = 'SELECT * FROM Problems'; db.all(sql, [], (err, rows) => { rows.forEach((rowQuestion) => { let arrayWithQuestionsId = _.split(rowQuestion.problem_questions_id, ',') var arrayOfAnswers = [] arrayWithQuestionsId.forEach((id) => { let sql = `SELECT * FROM QuestionsAndAnswersOfProblems WHERE question_id = ?` db.get(sql, [id], (err, rowAnswer) => { console.log(rowAnswer) // Object arrayOfAnswers.push(rowAnswer) }) // db.get(...) console.log(arrayOfAnswers) // [] }) // arrayWithQuestionsId.forEach(...) rowQuestion.answer = arrayOfAsnwers; }) // rows.forEach(...) console.log(rows) // [objects with 'answer': []] }) // db.all(...)个对象并添加rowQuestion字段而不是answer: [array of objects] rowQuestion

Answer 1

您拨打db.get()以获取答案是异步的，这意味着您的console.log(rows)在填充答案之前正在执行。当“行”处理完毕后，您将需要使用回调。

db.all(sql, [], (err, rows) => {
  // track the index here with a second parameter of "index"
  rows.forEach((row, index) => {
    // loop over the problem_questions_id
    _.split(row.problem_questions_id, ',').forEach((id) => {
      let sql = `SELECT * FROM QuestionsAndAnswersOfProblems WHERE question_id = ?`;
      // use db.all not db.get to fetch an array of answers
      // this call is asynchronous so we need to check if we are done inside the callback
      db.all(sql, [id], (err, answers) => {
         // "answers" is an array here
         row.answer = answers;
         // if the index is one less than the length it's the last
         if (index === rows.length-1) {
           // we're done!
           done(rows);
         }
      });
    });
  });
});

// this is called asynchronously when all the answers have been fetched
function done(rows) {
  console.log(rows);
}

保存节点的sqlite3包的结果

1 个答案: