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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.

Screenshot 2024-04-23 132412.png

        Then write the following code

const express = require("express");
const app = express();
const port = 5000;


app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});
  1. Import the mysql library to your project.
const mysql = require("mysql2");
  1. 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",
});
  1. 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");
  }
});

The code

const express = require("express");
const app = express();
const mysql = require("mysql2");
const port = 5000;

const connection = mysql.createConnection({
  host: "server2.mixkoap.com",
  port: "6105",
  user: "user",
  password: "password",
  database: "csc105-workshop",
});

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

// GET `/` (http://127.0.0.1:5000/ or http://localhost:5000/)
app.get("/", (req, res) => {
  return res.status(200).json({
    success: true,
    data: "Welcome to the example API",
    error: null,
  });
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});
  1. 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. ✅👇🏻

Screenshot 2024-04-23 134128.png

Let's write the endpoint that query todo-listuser 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 using 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. 👇🏻
app.get("/balance", 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 todo_id 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",
		});
	}
});
  1. Let's run your application again, and use postman with  localhost:5000/balance?userId=1
  • You will see the result like this.

Screenshot 2024-04-23 171658.png

Another example of Read

  1. Now let's try to create another endpoint, which is /users/all from the code below.
app.get("/users/all", 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",
		});
	}
});

    Example of Create 

    1. Create a endpoint that will create.

    • This is how query parameter works in URL 👆🏻
    • In this code, we have ...
    const todoId = req.query.todo_id;
    
    • that be a query parameter for this endpoint.
    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: 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,
            });
          }
        }
      });
    });
    
    • Let's try sending a request by creating a new request at Postman

     

    • 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

    1. 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

    1. 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

    1. 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,
      });
    });