回调后访问 RowDataPacket 时的奇怪行为答案

【问题标题】：Weird behavior when accessing RowDataPacket after a callback回调后访问 RowDataPacket 时的奇怪行为
【发布时间】：2020-05-07 11:24:33
【问题描述】：

我有以下函数来检索一个 sql 行对象。

function KnownConditionByUserFarm(d, callback) {
    var where = [
        d.user_hash,
        d.id,
        d.icon,
        d.days_since,
    ]

    sql = "SELECT id, NOW() as now, time, FROM_UNIXTIME(time), date_created, DATEDIFF(NOW(), FROM_UNIXTIME(time)) as days_since FROM weathers WHERE user_hash = ? AND farm_id = ? AND icon = ? AND time > UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL ? DAY));"

    query = db.query(sql, where, function (err, result) {
        if (err) {
            return callback(err, null)
        } else {
            return callback(null, result)
        }

    });
}

我可以在我的处理器功能上检索它，并且可以执行 console.log。

KnownConditionByUserFarm(data, (error, cond) => {

    if (error) {
        console.log("KnownConditionByUserFarm.Error:")
        console.log(error)
        process.exit()
    } else {

        console.log("KnownConditionByUserFarm/result")
        console.log(cond) // <-- can be accessed

    }
})

console.log(cond)的结果

KnownConditionByUserFarm/result
[ RowDataPacket {
    id: 19,
    now: 2020-05-07T03:10:20.000Z,
    time: 1587772800,
    'FROM_UNIXTIME(time)': 2020-04-24T16:00:00.000Z,
    date_created: 2020-04-24T22:16:13.000Z,
    days_since: 12 } ]

但是，当我尝试访问对象的其余部分（如 id、day_since）时，我收到以下错误。

代码

console.log(cond[0].id)

错误

KnownConditionByUserFarm/result
[ RowDataPacket {
    id: 19,
    now: 2020-05-07T03:14:51.000Z,
    time: 1587772800,
    'FROM_UNIXTIME(time)': 2020-04-24T16:00:00.000Z,
    date_created: 2020-04-24T22:16:13.000Z,
    days_since: 12 } ]
19 <-- I was able to access, but it's returning cannot read property.
KnownConditionByUserFarm/result
[]
***Parser.js:437
      throw err; // Rethrow non-MySQL errors
      ^

TypeError: Cannot read property 'id' of undefined

我能够访问id，但它抛出了一个奇怪的TypeError: Cannot read property 'id' of undefined。

请注意，我什至尝试过

var w = JSON.parse(JSON.stringify(cond))
console.log(w[0])

结果如下：

{ id: 19,
  now: '2020-05-07T03:22:24.000Z',
  time: 1587772800,
  'FROM_UNIXTIME(time)': '2020-04-24T16:00:00.000Z',
  date_created: '2020-04-24T22:16:13.000Z',
  days_since: 12 }

当我访问id时

console.log(w[0].id)

结果：

*/Parser.js:437
      throw err; // Rethrow non-MySQL errors
      ^

TypeError: Cannot read property 'id' of undefined

可能缺少什么？

【问题讨论】：

标签： javascript node.js callback node-mysql

【解决方案1】：

我不知道我遇到的问题可能是什么原因，但我能够通过再次执行并仔细记录来解决它，直到我得到我需要的。

var w = JSON.stringify(cond[0])
console.log(w)

var p = JSON.parse(w)
console.log(p)

console.log(p.id)
console.log(p.days_since)

var ps = JSON.parse(JSON.stringify(cond[0]))
console.log(ps.days_since)

【讨论】：