MacLochlainns Weblog

Sometimes, you just half to chuckle. A couple folks felt that I didn’t give enough information in my post showing how to configure a small Node.js application that could access a MySQL database. Specifically, they wanted me to explain the following:

1. Configure your Express.js and MySQL development in a single Node.js application.
2. How to convert the list of RowDataPacket objects as elements of data, which is really just simple JavaScript knowledge.
3. How to bind variables into the query.

Like the other blog post, this one assumes you’ve performed a global install of Node.js on a Linux server. If you’re unfamiliar with how to perform a global Node.js installation, I cover how to do it in this earlier blog post.

Before you write the Node.js applicaiton, you need to setup a db developer directory. A global install of Node.js means you need to create a node_modules symbolic link to the /usr/local/lib/node_modules directory in the db directory (in Linux). You can use the following Linux command from within the db directory to create the appropriate symbolic link:

ln -s /usr/local/lib/node_modules `pwd`/node_modules

or, assuming you have a /home/some_user/db directory

ln -s /usr/local/lib/node_modules /home/some_user/node_modules

After creating the node_modules symbolic link, you need to run the following two npm commands. Please note that second command holds the secret-sauce for generating a package.json file that supports Express.js and the MySQL driver:

npm init --y
sudo npm install --save express mysql

Then, you need to replace the package.json file with the contents of the package-lock.json file from your last npm command.

Here’s a small sample program that uses Express.js, converts the RowDataPackets collection, and binds local variables into the query:

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// Require libraries.
const express = require('express') 
const mysql = require('mysql')
 
// Create a mysql connection. 
const connection = mysql.createConnection({ 
  host: 'localhost', 
  user: 'student', 
  password: 'student', 
  database: 'studentdb' 
}) 
 
// Declare two local variables.
const start_date = '2001-01-01' 
const end_date = '2003-12-31' 
 
// Connect and display results in the console log.
connection.connect((err) => { 
if (err) 
  throw err 
else { 
  console.log('Connected to MySQL Server!\n') 
  connection.query("SELECT   i.item_title " + 
                   ",        date_format(i.release_date,'%d-%M-%Y') AS release_date " + 
                   "FROM     item i JOIN common_lookup cl " + 
                   "ON       i.item_type = cl.common_lookup_id " + 
                   "WHERE    cl.common_lookup_type = 'BLU-RAY' " + 
                   "AND      i.release_date BETWEEN ? AND ? " + 
                   "ORDER BY i.release_date" 
                  ,[start_date, end_date], function (err, result) { 
    if (err) 
      throw err 
    else { 
      // Prints the index value in the RowDataPacket. 
      for(let element in result) { 
        console.log(result[element].item_title + ', ' + result[element].release_date) 
      } 
      console.log('') 
      console.log('Press Ctrl-C to terminate ...') 
    } 
  }) 
} 
})

Line 28 shows two question marks. They act as placeholders for binding variables. Then, on line 30 you see a collection of the start_date and end_date local variables, which is the second argument to the query() function.

Rather than define individual variables, you can pass them as a collection directly. For example, you replace lines 14 and 15 with this single line:

14

const dates = ['2001-01-01','2003-12-31']

Then, you can pass dates as the second argument to the query() function, like this:

30

                  ,dates, function (err, result) {

Lines 35 and 36 show you how to convert a collection of RowDataPacket objects into elements of data. The for loop assigns the index value to the element variable, which lets you address a single RowDataPacket object instance. The dot (“.“) notation lets you use the name in a name-value pair to reference its value.

It displays the following:

Connected to MySQL Server! 
 
Star Wars II, 16-May-2002 
Harry Potter and the Chamber of Secrets, 28-May-2002 
Harry Potter and the Sorcerer's Stone, 28-May-2002 
Die Another Day, 03-June-2003 
 
Press Ctrl-C to terminate ...

Naturally, I’ll get around to writing something up that shows how to leverage MySQL data into a dynamic form with Handlebars at some point in the near future.

As always, I hope this helps those looking for a solution.