Server-Side Scripting/Document Databases/Node.js (Express)

routes/lesson10.js

// This program creates and displays a temperature database
// with options to insert, update, and delete records.
//
// References:
//  https://en.wikibooks.org/wiki/JavaScript
//  https://zellwk.com/blog/async-await-express/
//  https://docs.mongodb.com/drivers/node/usage-examples

const express = require("express");
const fs = require("fs");
const handlebars = require('handlebars');
const mongodb = require("mongodb")
const router = express.Router();

// Requires a Mongo installation to manage the database.
// Use of a Docker container is recommended.
// See https://en.wikiversity.org/wiki/Docker/MongoDB .
// If both the Node website and Mongo are running in containers, 
// use 172.17.0.2 for the mongodb host address.
// If the Node website and/or Mongo are running locally, use 127.0.0.1
// for the mongodb host address.

// const HOST = "mongodb://172.17.0.2";
const HOST = "mongodb://127.0.0.1";
const DATABASE = "temperature";
const COLLECTION = "countries";

router.get("/", async (request, response) => {
    let result = "";

    try {
        result = await getData();
    }
    catch(error) {
        result = error;
    }

    let source = fs.readFileSync("./templates/lesson10.html");
    let template = handlebars.compile(source.toString());
    let data = {
        table: result
    }
    result = template(data);
    response.send(result);
});

router.post("/", async (request, response) => {
    let result = "";

    try {
        let country = request.body.country.trim();
        let temperature = request.body.temperature.trim();

        if (!await countryExists(country)) {
            await insertCountry(country, temperature)
        } else if (temperature != "") {
            await updateCountry(country, temperature)
        } else {
            await deleteCountry(country)
        }

        result = await getData();
    }
    catch(error) {
        result = error;
    }

    let source = fs.readFileSync("./templates/lesson10.html");
    let template = handlebars.compile(source.toString());
    let data = {
        table: result
    }
    result = template(data);
    response.send(result);
});

async function getData() {
    const client = new mongodb.MongoClient(HOST);
    await client.connect();
    const database = client.db(DATABASE);
    const collection = database.collection(COLLECTION);
    const documents = await getDocuments(collection);

    let result = "<table><tr><th>ID</th>";
    result += "<th>Country</th>";
    result += "<th>Temperature</th></tr>";
    for (i = 0; i < documents.length; i++) {
        result += "<tr><td>" + documents[i]._id + "</td>";
        result += "<td>" + documents[i].country + "</td>";
        result += "<td>"+ documents[i].temperature + "</td></tr>";
    }
    result += "</table>";
    await client.close();
    return result;
}

async function getDocuments(collection) {
    return new Promise(function(resolve, reject) {
       collection.find().toArray( function(err, documents) {
        if (err)
            reject(err);
        else
            resolve(documents);
        });
    });
}

async function countryExists(country) {
    const client = new mongodb.MongoClient(HOST);
    await client.connect();
    const database = client.db(DATABASE);
    const collection = database.collection(COLLECTION);
    const filter = {
        country: country
    };
    const count = await collection.countDocuments(filter);
    await client.close();
    return !!(count);
}

async function insertCountry(country, temperature) {
    const client = new mongodb.MongoClient(HOST);
    await client.connect();
    const database = client.db(DATABASE);
    const collection = database.collection(COLLECTION);
    const document = {
        country: country,
        temperature: temperature
    };
    await collection.insertOne(document);
    await client.close();
}

async function updateCountry(country, temperature) {
    const client = new mongodb.MongoClient(HOST);
    await client.connect();
    const database = client.db(DATABASE);
    const collection = database.collection(COLLECTION);
    const filter = {
        country: country
    };
    const update = {
        "$set": { "temperature": temperature }
    };
    await collection.updateOne(filter, update);
    await client.close();
}

async function deleteCountry(country) {
    const client = new mongodb.MongoClient(HOST);
    await client.connect();
    const database = client.db(DATABASE);
    const collection = database.collection(COLLECTION);
    const filter = {
        country: country
    };
    await collection.deleteOne(filter);
    await client.close();
}

module.exports = router;

templates/lesson10.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Lesson 10</title>
    <link rel="stylesheet" href="styles.css">
</head>

<body>
    <h1>Temperature Data Entry</h1>
    <p>Enter country and temperature. Enter again to update.</p>
    <p>Enter country without temperature to delete.</p>
    <form method="POST">
        <p><label for="country">Country:</label>
            <input type="text" id="country" name="country" required>
        </p>
        <p><label for="stop">Temperature:</label>
            <input type="text" id="temperature" name="temperature">
        </p>
        <p><input type="submit" name="submit" value="Submit"></p>
    </form>
    <hr>
    {{{table}}}
</body>

</html>

Try It

See Server-Side Scripting/Routes and Templates/Node.js (Express) to create a test environment.