Question

脚本一直运行到尝试关闭数据库连接为止，现在它给了我一个Promise错误。

当我注释掉本节时，脚本可以正常运行而没有错误，但是，数据库连接永远不会关闭...

>     // .then(() => {
>     //   database.close();
>     // }, err => {
>     //   return database.close().then(() => {throw err; });
>     // })

在promise链的末尾仅有一个catch块还不够吗？

我收到以下错误：

[错误]（节点：9376）UnhandledPromiseRejectionWarning：未处理承诺拒绝。此错误是由以下原因引起的：一个没有catch块的异步函数，或者通过拒绝一个Promise 无法使用.catch（）处理。（拒绝ID：1） [[09：33：03.101]] [错误]（节点：9376）[DEP0018]弃用警告：已弃用未处理的诺言拒绝。将来，保证未处理的拒绝将终止Node.js进程退出代码为非零。

mysql.js

const mysql = require("mysql");

const mySQLConnectionDetails = {
  host: "localhost",
  user: "xxxx",
  password: "xxxx",
  database: "amdm",
  multipleStatements: true
};

class Database {
  constructor(config) {
    this.connection = mysql.createConnection(config);
  }
  query(sql, args) {
    return new Promise((resolve, reject) => {
      this.connection.query(sql, args, (err, rows) => {
        if (err)
          return reject(err);
        resolve(rows);
      });
    });
  }
  close() {
    return new Promise((resolve, reject) => {
      this.connection.end(err => {
        if (err)
          return reject(err);
        resolve();
      });
    });
  }
}
module.exports = { Database, mySQLConnectionDetails };

index.js

require("console-stamp")(console, "[HH:MM:ss.l]");
const express = require("express");
const router = express.Router();
const { Database, mySQLConnectionDetails} = require("../helpers/mySQL");
const { cleanseString, cleanseStringToArray, generateCountDuplication, sortValuesBykey, generateScoreArray, calculateAverage, replaceAbbreviationWithExpansion } = require("../helpers/stringFixers");

const database = new Database(mySQLConnectionDetails);


/* GET Clean original name of part and store it in database. */
router.get("/createcleanname", (req, res) => {
  let allParts = [];
  let eClassCodes = []; // here I define eClassCodes
  let abbreviationsAndExpansions = [];


  database.query("SELECT * FROM partnumbersclassified")
    .then(rows => {
      console.log(rows.length);
      allParts = rows;
      return database.query("SELECT * FROM amdm.abbreviationexpansion");
    })
    .then(rows => {
      abbreviationsAndExpansions = rows;
      return database.query("SELECT * FROM eclasstree WHERE numberofdigits = '8'");
    })
    .then(rows => {
      eClassCodes = rows; // Here I assign the values to the variable.
      const replaceAbbreviations = replaceAbbreviationWithExpansion(allParts, abbreviationsAndExpansions);
      console.log("replaceAbbreviations finished");
      const cleanseStrings = cleanseString(replaceAbbreviations, "cleanname");
      console.log("cleanseStrings finished");
      return cleanseStrings;
    })
    .then(result => {
      result.forEach(obj => {
        return database.query(`UPDATE partnumbersclassified SET cleanname = '${obj.cleanname}' WHERE itemnumber = '${obj.itemnumber}'`);
      });
      console.log("cleanname updated on all parts");
    })
    .then(() => {
      database.close();
    }, err => {
      return database.close().then(() => {throw err; });
    })
    .catch(err => {throw err;});
});

Answer 1

与其在catch中抛出错误，不如做它打算的：处理错误。

在您的情况下，您可能只想记录错误。

.then(() => {
    database.close();
  }, err => {
    return database.close().then(() => {throw err; });
  })
  .catch(err => {
    console.log(err)
  })

在生产环境中，您可能想使用Sentry之类的错误跟踪器来记录和处理错误。

为什么会收到UnhandledPromiseRejectionWarning：未处理的承诺被拒绝？

1 个答案: