Promises 问题：尝试包装 mysql 查询以在 NodeJS/Express 上使用它

Question

我的目标是包装 MySQL 查询，将参数传递给一个函数，另一个函数完成 MySQL 的工作，并返回结果。

到目前为止，这是我的代码：

//mysql lib
var mysql = require('mysql');

//database credentials
exports.pool = mysql.createPool({
connectionLimit: 50,
host: 'localhost',
user: 'root',
password: 'password',
database: '_app',
debug: false
});

//my wrapper =(
var returnResultset = exports.returnResultset = function (qry) {
return new Promise(function (resolve, reject) {
    try {

        mysql_.pool.getConnection(function (err, connection) {

            if (err) {
                console.log("Error on function returnResultset - MYSQL ERROR: " + err);
                return reject(err);
            }

            connection.query(qry, [], function (error, results, fields) {

                connection.release();

                if (error) {
                    console.log("Error on function returnResultset - MYSQL ERROR: " + error);
                    return reject(error);
                }

                return resolve(results);

            });

        });

    }
    catch (e) {
        console.log('error:' + e);
    }
});

};

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

returnResultset(qry_).then(function (results) {
    return results;
}, function (error) {
    console.log("Error: " + error);
})

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

var rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod);

console.log(rtf);

return rtf;

};

上面的代码返回undefined。我无法使此功能正常工作。

我试过console.log(results)。查询就像一个魅力。我唯一不能开始工作的就是从外部函数中捕获结果。

有什么想法吗？提前致谢！

Answer 1

您应该返回承诺并将其链接到 isExpired 函数中。

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

return returnResultset(qry_);

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

return db_.selectOneField('view_expiredusers', 'cod', 'cod', cod)



};

当你在其他文件中调用 isExpired 时，你应该使用 promise 的 then 方法并返回结果。如下操作

var cod_customer = 1;
var isexpired;
 isExpired(cod_customer).then(function (results) {
        isexpired = results;
        console.log(isexpired);
    }, function (error) {
        console.log("Error: " + error);
    });

Answer 2

你没有在 selectOneField 函数中返回承诺，它必须返回承诺，你也不能简单地这样做

rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod);

.你将不得不使用 async-await 或 then

必须这样处理

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

return returnResultset(qry_).then(function (results) {
    return results;
}).catch(error) {
    console.log("Error: " + error);
})

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

var rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod).then(rtf => {
console.log(rtf);

return rtf;
});


};