5 PHP techniques which you shouldn't use

We all have good and "not so good" coding habits. So let's reduce the bad ones step by step.

In this post you can see 5 BAD practices used by many PHP programmers and their correct alternative.

1. Do not hardcode widely used strings

(put them all in the config file)

Bad practice:

mailExample.php

================
$mail = new PHPMailer();
$mail->IsSMTP();
$mail->CharSet = 'UTF-8';
$mail->Host = 'smtp.example.com';
$mail->SMTPAuth = true;
$mail->Username = 'user';
$mail->Password = 'password';
$mail->AddReplyTo('contact@example.com', 'Support Team');
$mail->AddAddress($email, "{$firstname} {$lastname}");
$mail->SetFrom('contact@example.com', 'Support Team');
$mail->Subject = "Email subject";
$mail->AltBody = '';
$mail->Body = $txt_body;
if ($mail->Send()) {
 //Do something
}
================

Good practice:

config.php

================
define('SMTP_HOST', 'smtp.example.com');
define('SMTP_USERNAME', 'user');
define('SMTP_PASSWORD', 'password');
define('SMTP_EMAIL_FROM', 'contact@example.com');
define('SMTP_EMAIL_FROM_NAME', 'Support Team');
================

mailExample.php

================
require_once('config.php');
$mail = new PHPMailer();
$mail->IsSMTP();
$mail->CharSet = 'UTF-8';
$mail->Host = SMTP_HOST;
$mail->SMTPAuth = true;
$mail->Username = SMTP_USERNAME;
$mail->Password = SMTP_PASSWORD;
$mail->AddReplyTo(SMTP_EMAIL_FROM, SMTP_EMAIL_FROM_NAME);
$mail->AddAddress($email, "{$firstname} {$lastname}");
$mail->SetFrom(SMTP_EMAIL_FROM, SMTP_EMAIL_FROM_NAME);
$mail->Subject = "Email subject";
$mail->AltBody = '';
$mail->Body = $txt_body;
if ($mail->Send()) {
 //Do something
}
================

2. Avoid running MySQL "select" queries inside loops

(Select all the rows in one query and then build the needed array with PHP)

Bad practice:

example.php

================
$finalResult = array();
$categories = mysql_query("SELECT * FROM `tbl_categories`;");
while ($category = mysql_fetch_array($categories, MYSQL_ASSOC)) {
  $categoryProducts = mysql_query("SELECT * FROM `tbl_products` WHERE `category_id` = '".$category['id']."';");
  while ($product = mysql_fetch_array($categoryProducts, MYSQL_ASSOC)) {
   $finalResult[$category['id']][$product['id']] = $product['name'].' ('.$category['name'].')';
  }
}
================

Good practice:

example.php

================
$finalResult = array();
$result = mysql_query(
  "SELECT
   `c`.`id` AS `category_id`, `c`.`name` AS `category_name`,
   `p`.`id` AS `product_id`, `p`.`name` AS `product_name`
  FROM `tbl_categories` AS `c`
  JOIN `tbl_products` AS `p`
   ON `p`.`category_id` = `c`.`id`;
");
while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
  $finalResult[$row['category_id']][$row['product_id']] = $row['product_name'].' ('.$row['category_name'].')';
}
================

3. Don't overuse the server resources

(Optimize your code and execute every part of it only when it's necessary)

Bad practice:

example.php

================
$getCategories = (bool)$_GET['categories'];
$categories = mysql_query(/*Very heavy SQL query*/);
if ($getCategories) {
  while ($category = mysql_fetch_array($categories, MYSQL_ASSOC)) {
    //Some logic
  }
}
================

Good practice:

example.php

================
$getCategories = (bool)$_GET['categories'];
if ($getCategories) {
  $categories = mysql_query(/*Very heavy SQL query*/);
  while ($category = mysql_fetch_array($categories, MYSQL_ASSOC)) {
    //Some logic
  }
}
================

4. Don't invent your own coding style

(Keep the standards: indents, spaces, naming, comments)

Bad practice:

example.php

================
function gpi($pi, $ct = 'image')

{
if (isset($pi)){
$pif = '';
switch ($ct) {
case 'image' : {
// Some code
break;
}
case 'text' : {
// Some code
break;
}
default : {
// Some code
break;
}
}
return $pif;
} else {
return false;
}
}
================

Good practice:

example.php

================
/**
 * This function will get from database the description of a needed
 * product and will return the formatted version of it
 * in dependence of the $contentType.
 *
 * @param $productId The ID of the product
 * @param string $contentType The content type
 * @return bool|string In case the function is called wrong it will return false, otherwise - product description
 */
function getProductInfo($productId, $contentType = 'image') {
    if (isset($productId)){
        $productInfo = '';
        switch ($contentType) {
            case 'image' : {
                // Some code
                break;
            }
            case 'text' : {
                // Some code
                break;
            }
            default : {
                // Some code
                break;
            }
        }
        return $productInfo;
    } else {
        return false;
    }
}
================

5. Don't mix different types of logic

(Split your logic following the MVC architecture)

Don't write your PHP/MySQL, HTML, CSS and JavaScript code in the same file. Each of these should be split into different files. Also the PHP files should be split at least into 2 parts: the database controller part which executes MySQL queries and the logical part.