在Node中与MySQL结果异步/等待问题

如何解决在Node中与MySQL结果异步/等待问题

我有以下代码，这是通过Express进行的API调用。我需要返回一个引号数组，以及与这些引号关联的零件数组。为此，我使用的是async / await，它在自己的quotes变量中可以正常工作，但是我在parts变量中得到一个空数组。

我认为这与零件结果待定的承诺有关，因为当我在循环中控制台记录我的结果时，我会得到适当的值。

我怀疑我一定会误解async / await是如何工作的，或者promises / Promise.all是如何工作的。

感谢您帮助我理解为什么我没有兑现承诺的结果！

router.get('/:pagenum/:dealerno/:modelyear/',async (req,res) => {
  let quotes = await getQuotes(
    req.params.pagenum,req.params.dealerno,req.params.modelyear
  );

  console.log('MY QUOTES:');
  console.log(quotes); //This returns an array of my quotes,as expected

  let parts = await getQuoteParts(quotes);

  console.log('MY PARTS:');
  console.log(parts); //This returns an array of undefined values
});

function getQuotes(pagenum,dealerno,modelyear) {
  // return new Promise(function (resolve,reject) {
  var q_quote =
    "SELECT quote.id,DATE_FORMAT(quote.timestamp,'%b %d,%Y') AS timestamp,quote.quotenum,quote.quotetype,quote.configtype,quote.sid,quote.tractortype,customer.cus_id,customer.customername,parts.partno,units.type AS fmtype,combos.type AS mmtype FROM GH_savedquoteinfo AS quote JOIN GH_internal_customers AS customer ON quote.cusid=customer.cus_id JOIN GH_savedquoteparts AS parts ON (quote.quotenum = parts.quotenum AND parts.type='unit') LEFT JOIN " +
    modelyear +
    "_fm_units AS units ON (parts.partno = units.model_no AND quote.tractortype='FM') LEFT JOIN " +
    modelyear +
    "_mm_combos AS combos ON (parts.partno = combos.model_no AND quote.tractortype='MM') WHERE quote.dealerno=? AND quote.modelyear=? AND quote.quotetype!='multi' ORDER BY quote.quotenum LIMIT 7 OFFSET 0;";

  let resultHolder = [];

  return new Promise((resolve,reject) => {
    connection.query(q_quote,[dealerno,modelyear],function (
      err_quote,result_quote
    ) {
      if (err_quote) {
        console.log('error');
      } else {
        try {
          resultHolder.push(result_quote);
        } catch (e) {
          console.log('error');
        } finally {
          resolve(resultHolder);
        }
      }
    });
  });
}

async function getQuoteParts(quoteResult) {
  let quoteParts = [];
  let quotePartsResult = await Promise.all(
    quoteResult[0].map(async (quote,index) => {
      var q_parts =
        "SELECT * FROM GH_savedquoteparts WHERE quotenum=? AND (type='' OR type='pvcomplete') ORDER BY id";

      connection.query(q_parts,[quote.quotenum],function (
        err_parts,result_parts
      ) {
        if (err_parts) {
          console.log('error in parts' + err.message);
        } else {
          console.log(result_parts); //This returns an array of my parts
          quoteParts.push(result_parts);
        }
      });
    })
  );

  return quoteParts; 
}

解决方法

获得未定义值数组的原因是因为您返回的是quotePartsResult而不是要推送值的quoteParts。由于您正在quoteResult上运行.map，并且没有在map函数内部返回任何内容，因此它将解析为undefined。

我想重构您的代码以更好地理解。您应该在Promise.all（）调用中包含一个Promise数组。

类似的东西：

const promises = qouteResult.map(async (quote) => {
  // Your query calls. You can also promisify the callbacks in here using 
  util.promisify()
});

OR

const promises = qouteResult.map(qoute => {

return new Promise((resolve,reject) => {
  // Your query calls.
  if(success) {
    resolve()
  } else {
    reject()
  }
});
});

const result = await Promise.all(promises);
return result;

,

正如评论中提到的某个人，我最想念的是围绕我的第二个连接的一个新的Promise包装器。我还需要第二个函数getQuoteParts中的Promise.all。最终代码如下：

router.get('/:pagenum/:dealerno/:modelyear/',async (req,res) => {
  //QUOTES ARRAY
  const quotes = await getQuotes(
    req.params.pagenum,req.params.dealerno,req.params.modelyear
  );

  const parts = await getQuoteParts(quotes);

  const details = await getPartDescrips(parts,quotes);

  Promise.all([quotes,parts,details]).then((results) => {
    res.send(results);
  });
});

function getQuotes(pagenum,dealerno,modelyear) {
  // return new Promise(function (resolve,reject) {
  const qQuote =
    "SELECT quote.id,DATE_FORMAT(quote.timestamp,'%b %d,%Y') AS timestamp,quote.quotenum,quote.quotetype,quote.configtype,quote.sid,quote.tractortype,customer.cus_id,customer.customername,parts.partno,units.type AS fmtype,combos.type AS mmtype FROM GH_savedquoteinfo AS quote JOIN GH_internal_customers AS customer ON quote.cusid=customer.cus_id JOIN GH_savedquoteparts AS parts ON (quote.quotenum = parts.quotenum AND parts.type='unit') LEFT JOIN " +
    modelyear +
    "_fm_units AS units ON (parts.partno = units.model_no AND quote.tractortype='FM') LEFT JOIN " +
    modelyear +
    "_mm_combos AS combos ON (parts.partno = combos.model_no AND quote.tractortype='MM') WHERE quote.dealerno=? AND quote.modelyear=? AND quote.quotetype!='multi' ORDER BY quote.quotenum DESC LIMIT 7 OFFSET 0;";

  let resultHolder = [];

  return new Promise((resolve,reject) => {
    connection.query(qQuote,[dealerno,modelyear],function (
      errQuote,resultQuote
    ) {
      if (errQuote) {
        console.log(errQuote.message);
      } else {
        try {
          resolve(resultQuote);
        } catch (e) {
          console.log(e.message);
        }
      }
    });
  });
}

function getQuoteParts(quoteResult) {
  var partResults = quoteResult.map((quote,index) => {
    return new Promise((resolve,reject) => {
      const qParts =
        "SELECT * FROM GH_savedquoteparts WHERE quotenum=? AND (type='' OR type='pvcomplete') ORDER BY type='pvcomplete',type='',id";
      // new Promise((resolve,reject) => {
      connection.query(qParts,[quote.quotenum],function (
        errParts,resultParts
      ) {
        if (errParts) {
          console.log('error in PARTS');
        } else {
          resolve(resultParts);
        }
      });
    });
  });

  return Promise.all(partResults);
  
}

我写了一篇文章，概述了它在这里的工作方式： https://medium.com/@amymurphy_40966/node-mysql-chained-promises-vs-async-await-9d0c8e8f5ee1