Example of Read

Let's write the endpoint that query user balance data from the database and response to the user.

• This the schema of sample database 👇🏻

1. Let's create a first endpoint query balance from the database by create getBalance.js in controller->transaction directory

then use the code below.

• In the path /balance, it will query from balance of the users table.
• We will use the .query() method to insert your SQL query.
• The second argument to the .query() method is a callback function (err, rows), which will be called when the MySQL send the response. The callback function takes two arguments, err and rows, which represent the error of the database and rows objects for response data from MySQL database.
• If we found an error, we will response the error message to the client.
• else, we will return row which is data from the users table from the database. 👇🏻

const connection = require("../../services/database");

const getBalance = async (req, res) => {
	// Assign the params as a variable
	const userId = req.query.userId;

	// Regex to check the userId is a number only or not
	const checkUserId = new RegExp(/^\d+$/).test(userId); // Boolean

	// Check if the userId is not exist or is not a number, return json with an error
	if (!userId || !checkUserId) {
		return res.json({
			success: false,
			data: null,
			error: "user_id is invalid",
		});
	}
	// Query the data from the database
	try {
		// Get user balance data
		const userBalanceQuery = await connection
			.promise()
			.query(`SELECT balance FROM users WHERE id = ${userId}`);
		const userBalance = userBalanceQuery[0][0];
		// Check if user data is empty
		if (!userBalance) {
			return res.status(404).json({
				success: false,
				data: null,
				error: "User not found",
			});
		}
		// Return data to the client if success
		return res.json({
			success: true,
			data: userBalance,
			error: null,
		});
	} catch (error) {
		console.error("Error:", error);
		return res.status(500).json({
			success: false,
			data: null,
			error: "Internal server error",
		});
	}
};

module.exports = getBalance;

2. Create transaction.js under routers and create router for transaction

const express = require("express");
const getBalance = require("../controllers/transactions/getBalance");
const transactionsRouter = express.Router();

transactionsRouter.get("/balance", getBalance);

module.exports = transactionsRouter;

3. Import transactionsRouter into index.js and make a path

const express = require("express");
const app = express();
//add this line 👇
const transactionsRouter = require("./routers/transactions");
const port = 5000;
app.use(express.json());
//add this line 👇
app.use("/transactions", transactionsRouter);
app.listen(port, () => {
	console.log(`Example app listening on port ${port}`);
});

4. Let's run your application again, and use postman with  localhost:5000/transactions/balance?userId=1

• You will see the result like this.

Another example of Read

1. Create getAll.js under directory controller->users

2. Create an endpoint query all users from the database using the code below in getAll.js

const connection = require("../../services/database");

const getAll = async (req, res) => {
	// Query the data from the database
	try {
		// Get user data
		const userDataQuery = await connection
			.promise()
			.query(`SELECT * FROM users`);
		const userData = userDataQuery[0];

		// Check if user data is empty
		if (!userData) {
			return res.status(404).json({
				success: false,
				data: null,
				error: "There is no user data in the database",
			});
		}
		// Return data to the client if success
		return res.json({
			success: true,
			data: userData,
			error: null,
		});
	} catch (error) {
		console.error("Error:", error);
		return res.status(500).json({
			success: false,
			data: null,
			error: "Internal server error",
		});
	}
};
module.exports = getAll;

3. Create users.js under directory routers and write

const express = require("express");
const getAll = require("../controllers/users/getAll");
const usersRouter = express.Router();

usersRouter.get("/all", getAll);

module.exports = usersRouter;

4. Import usersRouter into index.js and make a path

const express = require("express");
const app = express();
//add this line 👇
const usersRouter = require("./routers/users");
const transactionsRouter = require("./routers/transactions");
const port = 5000;
app.use(express.json());

//add this line 👇
app.use("/users", usersRouter);
app.use("/transactions", transactionsRouter);

app.listen(port, () => {
	console.log(`Example app listening on port ${port}`);
});

5. Let's run your application again, and use postman with  localhost:5000/users/all

• You will see the result like this.

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