NodeJS Promises 无法编辑现有 'model'

Question

编辑仔细检查后，似乎 async.forEach 在 getCurrencies 甚至运行第一次完成之前完成...我该如何解决这个问题？我认为返回一个 promise 基本上 'chain' 这些 promise 在一起？

我有以下代码，它试图从 mysql 读取交易。由于 table 的大小和查询所需的时间长度，我将其分解并使用 promises 来填充对象。但是，getCurrencies 不会更新模型的 currencyCode - 然而，console.log 都报告了正确的值。有人可以解释我做错了什么吗？我对承诺还很陌生。谢谢。

主要对象建筑

    connection.query(query).then(function(items) {
        async.forEach(items, function(element) {
            element.ptype = 'merchants';
            element.type = 'transactions';
            element.currencyCode = null;

            getCurrencies(element.currencies_id).then(function(result) {
                console.log(result.currencyCode);
                element.currencyCode = result.currencyCode;
                console.log(JSON.stringify(element));
            });
        });

        res.send(items);
    });

获取货币

function getCurrencies(transactionId) {
    var currencies_query = '';
    currencies_query += 'SELECT ';
    currencies_query += 'iso_code AS currencyCode, ';
    currencies_query += 'name AS `currencyName`, ';
    currencies_query += 'symbol AS `currencySymbol`, ';
    currencies_query += 'exponent AS `currencyExponent`, ';
    currencies_query += 'iso_num AS `currencyNumber` ';
    currencies_query += 'FROM ';
    currencies_query += 'currencies ';
    currencies_query += 'WHERE ';
    currencies_query += 'id = ' + transactionId;

    return new Promise(function(resolve, reject) {
        connection.query(currencies_query).then(function(rows) {
            resolve(rows[0]);
        });
    });
};

和 console.logs

的输出

先

GBP

秒

{"id":11213595,"pid":100856,"uri":"/rest/transactions/11213595","puri":"/rest/merchants/100856","path":"/resellers/1/customers/5/merchants/100856/transactions/11213595","transactionID":11213595,"currencies_id":1,"transactionUri":"/rest/transactions/11213595","ptype":"merchants","type":"transactions","currencyCode":"GBP"}

来自邮递员的 api 响应

{
    "id": 11213615,
    "pid": 103845,
    "uri": "/rest/transactions/11213615",
    "puri": "/rest/merchants/103845",
    "path": "/resellers/1/customers/2368/merchants/103845/transactions/11213615",
    "transactionID": 11213615,
    "currencies_id": 1,
    "transactionUri": "/rest/transactions/11213615",
    "ptype": "merchants",
    "type": "transactions",
    "currencyCode": null
  }

如您所见，currencyCode 仍然是 null - 为什么？！ :(

Answer 1

As you can see, currencyCode is still null - Why?! :(

我之前没有使用 "async.forEach"，但我认为 currencyCode 是 Null - 因为你调用了 promise "getCurrencies"，异步工作

如果您需要用很少的承诺来响应客户 - 您必须收集承诺到数组，然后调用 Promise.all（这将 return 所有承诺的结果数组)

并且您应该在下一个链块中发送响应。我认为它应该有效

connection.query(query)
.then(function(items) {
    var arPromises = [];
    async.forEach(items, function(element) {
        element.ptype = 'merchants';
        element.type = 'transactions';
        element.currencyCode = null;
        arPromises.push(
            new Promise(function (resolve, reject) {
                getCurrencies(element.currencies_id)
                    .then(function(result) {
                        element.currencyCode = result.currencyCode;
                        resolve(element);
                    }).catch(function (error) {
                        //do something with error
                        if(error)
                           reject(error);
                    });
            })
        );
    });
    return Promise.all(arPromises);
}).then(function(items){
    res.send(items);
}).catch(function (error) {
    if(error)
     console.log(error);
});

我的建议是，用 "catch" 块结束链 - 以避免丢失错误

NodeJS Promises 无法编辑现有 'model'

NodeJS Promises can't edit existing 'model'

javascript

mysql

node.js

promise

bluebird