Answered: the code that I have, I need to change…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

the code that I have, I need to change the endpont /specialOperation to asynchronously (with your utility module) get the grade result and rectangle result like this( promises required):

{"gradeStats":{"average":86.25,"minimum":73,"maximum":97},"rectangle":{"area":8,"perimeter":12}}

require('dotenv').config();

const calculator = require('./asyncCalculator');

const express = require('express');

const { response } = require('express');

const app = express();

app.get('/gradeStats', gradeStats);

app.get('/rectangle', rectangle);

app.get('/specialOperation', specialOperation);

const listener = app.listen(process.env.PORT, process.env.HOST, () => {

console.log(`Server listening at ${listener.address().address}:${listener.address().port}`);

});

function gradeStats(req, res) {

calculator.gradeStats(req.query.grade)

.then((result) => { res.json({ result: result }) })

.catch((error) => { res.status(400).json({ error: error.message }) });

}

function rectangle(req, res) {

const length = parseInt(req.query.length);

const width = parseInt(req.query.width);

calculator.rectangle(length, width)

.then((response) => { res.json({ result: response }) })

.catch((error) => { res.status(400).json({ error: error.message }) });

}

function specialOperation(req, res) {

const { length, width, grade: gradeString } = req.query;

calculator.specialOperation(gradeString, parseInt(length), parseInt(width))

.then(({result}) => { res.json({ result: result }) })

.catch((error) => { res.status(400).json({ error: error.message }) });

}

async function gradeStats(grade) {

const promise = new Promise((resolve, reject) => {

setTimeout(function() {

if (!grade) {

reject(new Error("Error: grade is undefined."));

return;

}

for (const g of grade) {

if (isNaN(g)) {

reject(new Error("Grades should only contain numbers."));

return;

}

const numGrades = grade.map(g => parseInt(g, 10));

const min = Math.min(...numGrades);

const max = Math.max(...numGrades);

const avg = (numGrades.reduce((a, b) => a + b) / numGrades.length).toFixed(2);

const result = { average: avg, minimum: min, maximum: max };

resolve(result);

}, 0);

});

return promise;

}

async function rectangle(length, width) {

const promise = new Promise((resolve, reject) => {

setTimeout(function() {

if (isNaN(length) || isNaN(width)) {

reject(new Error("Both length and width are required parameters." ));

} else if (length === undefined || width === undefined) {

reject(new Error("Both length and width are required parameters."));

} else if (length <= 0 || width <= 0) {

reject(new Error("Both length and width must be greater than 0." ));

} else {

const area = length * width;

const perimeter = 2 * (length + width);

const response = {area, perimeter};

resolve(response);

}

});

return promise;

}

async function specialOperation(gradeString, length, width) {

const promise = new Promise((resolve, reject) => {

const promise1 = new Promise((resolve, reject) => {

if (!gradeString) {

reject(new Error("Grades parameter is missing."));

return;

}

const grade = String(gradeString).split(",").map(Number);

const min = Math.min(...grade);

const max = Math.max(...grade);

const avg = (grade.reduce((a, b) => a + b) / grade.length).toFixed(2);

resolve({ average: parseFloat(avg), minimum: min, maximum: max });

});

const promise2 = new Promise((resolve, reject) => {

setTimeout(() => {

try {

const area = length * width;

const perimeter = 2 * (length + width);

resolve({ area, perimeter });

} catch (error) {

reject("An error occurred");

}

}, 2000);

});

Promise.all([promise1, promise2])

.then(([gradeStats, rectangle]) => {

const result = { gradeStats, rectangle };

resolve(result);

})

.catch((error) => {

reject(error);

});

}

function validateOperands(a, b, reject) {

if (a === undefined || b === undefined)

reject(new Error('Both a and b are required.'));

if (isNaN(a) || isNaN(b))

reject(new Error('Both a and b must be numbers.'));

}

module.exports = {

dotted,

fizzBuzz,

gradeStats,

rectangle,

specialOperation,

};

Expert Solution

Step 1 ans

Here's how you can modify the specialOperation function to use promises and make the necessary calls to gradeStats and rectangle asynchronously:

async function specialOperation(gradeString, length, width) {
const promise1 = new Promise((resolve, reject) => {
if (!gradeString) {
reject(new Error("Grades parameter is missing."));
return;
}
const grade = String(gradeString).split(",").map(Number);
calculator.gradeStats(grade)
.then((result) => resolve(result))
.catch((error) => reject(error));
});

const promise2 = new Promise((resolve, reject) => {
calculator.rectangle(length, width)
.then((result) => resolve(result))
.catch((error) => reject(error));
});

const [gradeStatsResult, rectangleResult] = await Promise.all([promise1, promise2]);
const result = { gradeStats: gradeStatsResult, rectangle: rectangleResult };
return result;
}

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