Week2 : DB connection & CRUD

Database connection

1. Let's start by creating an index.js then initializing your JavaScript project by running npm init in your terminal after that let's download the libraries that we will be using today which are express and mysql by running npm install express mysql2.

2. Create 3 directory which are routers, Controllers, services then create 2 directory transactions and users

3. Write the following code in the index.js

const express = require("express");
const app = express();
const port = 5000;
app.use(express.json());


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

4. In directory services create database.js

5. Import the mysql library to your project.

const mysql = require("mysql2");

6. Add the following code

This is the database configuration of your database.

const connection = mysql.createConnection({
  host: "tutorialdb.pspgun.com",
  port: "13308",
  user: "",
  password: "",
  database: "csc-105",
});

7. Connect to the database

This line of code is using the connection variable from above to connect to the database using .connect() method.

connection.connect((err) => {
  if (err) {
    console.log(err);
  } else {
    console.log("Database is connected");
  }
});

8. Export the connection so that we can use it in other file.

module.exports = connection;

The code right now should look like this in

const mysql = require("mysql2");

const connection = mysql.createConnection({
	host: "tutorialdb.pspgun.com",
	port: "13308",
	user: "mentor",
	password: "mentor1212312121",
	database: "csc-105",
});

// Connect to database
connection.connect((err) => {
	if (err) {
		console.log(err);
		throw "Database is not connected";
	} else {
		console.log("Database is connected");
	}
});

module.exports = connection;

9. Restart the application

If your database connection is invalid, it will show you an error. ❌👇🏻

If your database connection is valid, your application will run correctly. ✅👇🏻

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

This the schema of sample database 👇🏻

Example of Read

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
const transactionsRouter = require("./routers/transactions");
const port = 5000;
app.use(express.json());
// Add
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

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;

Example of Create

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

Create a request.

http://127.0.0.1:3000/todo?todo_id=1

Click Send

The response from your backend application 👇🏻

Example of the `POST` method

Create an endpoint that create a user

Before writing a request, we need to install the library body-parser first.

npm i body-parser

Because Express JS cannot read the JSON body request directly, So we need to install body-parser first.

const bodyParser = require("body-parser"); // import the body-parser

// parse various different custom JSON types as JSON
app.use(bodyParser.json({ type: "application/json" }));

Code ...

const express = require("express");
const app = express();
const mysql = require("mysql2");
const bodyParser = require("body-parser"); 👈🏻
const port = 3000;

const connection = mysql.createConnection({
  host: "server2.mixkoap.com",
  port: "6103",
  user: "root",
  password: "root_apisitmaneerat",
  database: "csc105-workshop",
});

// Connect to database
connection.connect();

console.log("Database is connected");

// parse various different custom JSON types as JSON
app.use(bodyParser.json({ type: "application/json" })); 👈🏻

app.get("/", (req, res) => {
  res.send("Hello World!");
});
.
.
.
.
.
.

Create an endpoint

app.post("/todo/create", (req, res) => {
  // The JSON body
  const payload = req.body;

  connection.query(
    `INSERT INTO users (username) VALUES (?)`, [payload.userName], (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        // Return data to the client if success
        console.log(rows);
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "create success",
            },
          });
        }
      }
    }
  );
});

The request body mostly send in JSON format 👆🏻

Create a request in Postman and change the HTTP method to POST

****Remark - HTTP Methods 👇🏻

Add the JSON body 👇🏻

http://127.0.0.1:3000/todo/create

{
    "userName" : "Apisit Maneerat"
}

Click Send

The response from your backend application. 👆🏻

In the Database 👇🏻

For more detail

Example of the `PATCH` method

Create an endpoint that edit the data in the Database

For example we are going to change the name and detail from id = 1

Create the endpoint

For this endpoint we use .patch() because we are going to edit some fields that you specific in the Database.

app.patch("/todo/edit", (req, res) => {
  // The JSON body
  const payload = req.body;

  console.log(payload);

  connection.query(
    "UPDATE items SET name = ?, detail = ? WHERE id = ?", [payload.name, payload.detail, payload.id],
    (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        // Return data to the client if success
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "update successfully",
            },
          });
        }
      }
    }
  );
});

Create a request in Postman

Click Send

Example of the `DELETE` method

Create an endpoint that delete the data from the links table in the database.

For this endpoint, we will use .delete() because we are going to delete data from the database.

We use query string to get the data from the client

Create an endpoint 👇🏻

app.delete("/todo/delete", (req, res) => {
  // Assign the params as a variable
  const id = req.query.id;
  const todoId = req.query.todo_id;

  connection.query(
    `DELETE FROM links where id = ? AND todo_id = ?`, [id, todoId],
    (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "delete successfully",
            },
          });
        }
      }
    }
  );
});

Create a request in Postman

Click Send

--- End of the example ----

** This is the finalized code for this example 👇🏻

const express = require("express");
const app = express();
const mysql = require("mysql2");
const bodyParser = require("body-parser");
const port = 3000;

const connection = mysql.createConnection({
  host: "server2.mixkoap.com",
  port: "6103",
  user: "root",
  password: "root_apisitmaneerat",
  database: "csc105-workshop",
});

// Connect to database
connection.connect();

console.log("Database is connected");

// parse various different custom JSON types as JSON
app.use(bodyParser.json({ type: "application/json" }));

app.get("/", (req, res) => {
  res.send("Hello World!");
});

app.get("/hello", (req, res) => {
  res.json({
    name: "Apisit Maneerat",
    nickName: "Mixko",
    university: "KMUTT",
  });
});

app.get("/todo/all", (req, res) => {
  connection.query("SELECT * FROM items", (err, rows) => {
    // Check if cannot find the data in the database then return the error
    if (err) {
      res.json({
        success: false,
        data: null,
        error: err.message,
      });
    } else {
      // Return data to the client if success
      res.json({
        success: true,
        data: rows,
        error: null,
      });
    }
  });
});

app.get("/todo", (req, res) => {
  // Assign the params as a variable
  // https://medium.com/@joseph.pyram/9-parts-of-a-url-that-you-should-know-89fea8e11713
  const todoId = req.query.todo_id;

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

  // Check if the todo_id is not exist or is not a number, return json with an error
  if (!todoId || !checkTodoId) {
    res.json({
      success: false,
      data: null,
      error: "todo_id is invalid",
    });
  }

  connection.query(`SELECT * FROM items WHERE id = ${todoId}`, (err, rows) => {
    // Check if cannot find the data in the database then return the error
    if (err) {
      res.json({
        success: false,
        data: null,
        error: `Data not found ${err.message}`,
      });
    } else {
      // Return data to the client if success
      if (rows[0]) {
        res.json({
          success: true,
          data: rows[0],
          error: null,
        });
      } else {
        res.json({
          success: true,
          data: null,
          error: null,
        });
      }
    }
  });
});

app.post("/todo/create", (req, res) => {
  // The JSON body
  const payload = req.body;

  connection.query(
    `INSERT INTO users (username) VALUES (?)`,
    [payload.userName],
    (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        // Return data to the client if success
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "create successfully",
            },
          });
        }
      }
    }
  );
});

app.patch("/todo/edit", (req, res) => {
  // The JSON body
  const payload = req.body;

  console.log(payload);

  connection.query(
    "UPDATE items SET name = ?, detail = ? WHERE id = ?",
    [payload.name, payload.detail, payload.id],
    (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        // Return data to the client if success
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "update successfully",
            },
          });
        }
      }
    }
  );
});

app.delete("/todo/delete", (req, res) => {
  // Assign the params as a variable
  const id = req.query.id;
  const todoId = req.query.todo_id;

  connection.query(
    `DELETE FROM links where id = ? AND todo_id = ?`,
    [id, todoId],
    (err, rows) => {
      // Check if cannot find the data in the database then return the error
      if (err) {
        return res.json({
          success: false,
          data: null,
          error: err.message,
        });
      } else {
        if (rows) {
          res.json({
            success: true,
            data: {
              message: "delete successfully",
            },
          });
        }
      }
    }
  );
});

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

More examples for those who want to create more than one query in one endpoint

app.get("/todo/from", async (req, res) => {
  const userId = req.query.userId;

  // User data
  const userData = await new Promise((resolve, reject) => {
    connection.query(
      `SELECT * FROM users WHERE id = ?`,
      [userId],
      (err, rows) => {
        if (err) {
          res.json({
            suceess: false,
            error: err.message,
          });
        } else {
          resolve(rows[0]);
        }
      }
    );
  });

  // User's todos
  const userTodos = await new Promise((resolve, reject) => {
    connection.query(
      `SELECT * FROM items WHERE owner_id = ?`,
      [userId],
      (err, rows) => {
        if (err) {
          res.json({
            suceess: false,
            error: err.message,
          });
        } else {
          resolve(rows);
        }
      }
    );
  });

  res.json({
    success: true,
    data: {
      user_data: userData,
      todos: userTodos,
    },
    error: null,
  });
});