Week2 : DB connection & CRUD

Database connection

Install the mysql library to your project, by enter the command line npm install mysql2

Import the mysql library to your project.

const mysql = require("mysql2");

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",
});

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 = 3000;

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");
  }
});

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

Restart the applcation

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 todo-list data from the database and response to the user.

This the schema of sample database 👇🏻

Example of `GET` method

Let's create a first endpont query all todo-list from the database.

In the path /todo/all, it will query from all data from items 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 items table from the database. 👇🏻

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
      return res.json({
        success: true,
        data: rows,
        error: null,
      });
    }
  });
});

Let's run your application again, and go to the path localhost:3000/todo/all

You will see the data that response to the client.

Let's install a program that you can test your API easier!

Go to download and install the Postman via https://www.postman.com/downloads/

Postman is an API platform for building and using APIs. Postman simplifies each step of the API lifecycle and streamlines collaboration so you can create better APIs—faster.

Open the Postman
Click +
Click Add a request to add a request.

(1) Name your request
(2) Enter your request path (localhost == 127.0.0.1)
(3) Click Send

After you clicked send, it will show the response data from your backend application. 👇🏻

You can use Postman to test your API from your backend application here. that easier than testing on your website. 😊

Let's back to our backend application.

Example of `query parameter` URL

Create a endpoint that query a todo-list by id using parameters from URL.

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

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,
  });
});

Week2 : DB connection & CRUD

Database connection

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

Example of GET method

Example of query parameter URL

Example of the POST method

Example of the PATCH method

Example of the DELETE method

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

Example of `GET` method

Example of `query parameter` URL

Example of the `POST` method

Example of the `PATCH` method

Example of the `DELETE` method