Browser image caching was causing me a problem today.
When a user of a client site uploads a profile image, it intentionally overwrites the old image. However, when viewing the profile page, the old image is shown unless you refresh the page.
Preventing browser image caching
The solution was quite simple. In order to force the browser to fetch the image from the server, I add a random number to a querystring at the end of the image name. Example:
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<p>A simple solution to preventing image caching.</p>
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Posted by admin in Web development, php
Tagged browser, caching, image, php, prevent
Multidimensional arrays are arrays which contain arrays and each of those may also contain arrays. There is no limit to the number or level of sub-arrays.
$stoves = array(
0=>array('Bronze',
'elements'=>array('4 rings', 'oven'),
),
1=>array('Silver',
'elements'=>array('4 rings', 'oven', 'grill'),
)
?>
End of Multidimensional Arrays.
Most of us know what general interview questions to expect, but sometimes we may not be as prepared for interview questions as we think we are. So, here are a few interview questions that I have been asked whilst at interviews for web developer roles:
- How do you keep up to date with trends and changes in web development?
- Can you show us some example code?
- What is the most complex application you have built?
- What is XSS?
- How would you prevent MySQL injection?
- What can you tell me about CSS sprites?
- What do you know about the CSS Box Model?
- What is a recursive function?
- Do you know what multi-dimensional arrays are?
These are just a few sample web developer interview questions
MySQL
MySQL Join Tables
The MySQL JOIN command allows you to acquire/manipulate data from more than one table in a single query statement.
MySQL JOIN commands can be used in SELECT, UPDATE and DELETE statements.
However, MySQL JOIN commands use a lot of database resources as they need conditional matches across all of the tables.
The Simple MySQL Join
This is the easiest of the Join queries. With this JOIN query you are basically conducting two separate queries on two related tables, but joining them into one query. The WHERE condition is used to connect corresponding results.
The syntax is as follows:
SELECT table_a.id, table_a.name, table_b.meals FROM table_a JOIN table_b WHERE table_a.name = table_b.name
In the join example above, you may use a comma in place of the word ‘JOIN‘.
The MySQL LEFT Join
Join Tables with MySQL
The LEFT JOIN is slightly more complicated that the simple join. By using a LEFT JOIN, as well as all records which match the WHERE condition, I also retrieve all the records from the first table (left of the join) which do not match the WHERE condition.
The syntax is as follows:
SELECT table_a.id, table_a.name, table_b.meals FROM table_a LEFT JOIN table_b ON table_a.name = table_b.name
The MySQL Inner Join
INNER JOIN behaves in the same way as LEFT JOIN except that if no matches are found, no results are created.
The syntax is as follows:
SELECT table_a.id, table_a.name, table_b.meals FROM table_a INNER JOIN table_b WHERE table_a.name = table_b.name
A week or so ago, another developer showed me the Nectar Points website (www.nectar.com) and pointed out that the webpages appear to have a custom suffix – in this case .nectar
So, how did they do it?
It appears that the website is on an Apache server, my guess is that they used the .htaccess ‘AddType’ directive.
The AddType Directive
The AddType directive allows you to specify what MIME type should be reported for specified file suffixes. This MIME type will then be used by the browser when serving up a web page having the specified suffix.
The syntax:
AddType mime-type file-extension
So, if I decide to change the suffix of any of my PHP files to ‘.beer’, then I will use this in the .htaccess file:
AddType application/x-httpd-php .beer
Now, pagename.beer will be treated by the browser like any other PHP file.
MySQL injection occurs when someone unauthorised attempts to run an MySQL statement on your database. This will normally take the form of inserting a MySQL statement where you would normally expect some user input – maybe their username.
MySQL Injection Prevention
There is a PHP function which can be used to prevent MySQL injection attacks:
mysql_real_escape_string($variable)
The mysql_real_escape_string() makes the string safe from MySQL injection by escaping any injection code in the data which is to be used in the MySQL query.
MySQL injection attempts normally have the single quote character(‘). mysql_real_escape_string() inserts a backslash in front of it to escape it.
Recursive functions are functions which call themselves. They are particularly useful when working with multi-dimensional arrays. However, using recursive functions should be avoided if the function is likely to be called over 200 times, as it may kill the script.
Here is a very basic example of how one could use a recursive function in PHP:
<?php
# This function iterates over the main array
# It checks each value and if not an array adds to variable
# If one of the values is an array the function calls itself
# and passes that sub array to itself (the function)
function total($numbers)
{
$total = FALSE; // initialise variable
foreach ($numbers as $number) {
if(is_array($number)) { //is the value an array
$total += total($number); //calls itself & passes sub array
} else { // not an array
$total += $number; // add values to variable
}
}
return $total;
}
$numberlist = array(10, 20, 5,
array(5, 2, 3)
);
$result = total($numberlist); // pass arrays to function
echo “Total = $result\n”;
?>
This example is a very basic recursive function.
CodeIgniter
CodeIgniter – created by EllisLabs and first released in 2006, CodeIgniter is a freely available MVC web application framework used for developing websites using PHP.
CodeIgniter ships with a large library commonly used OOP classes, enabling the developer to call them rather that using time creating her own. When compared to other similar MVC frameworks, CodeIgniter is said to be:
“..faster, lighter and the least like a framework.” Rasmus Lerdorf 2008
Benefits of CodeIgniter
- Get started quickly
- No need to install other packages
- No need for mass configuration
- Compatible with PHP 4 & 5
- Detailed user guide
- Enables faster cleaner development
- Easy to extend by adding your own classes
- It’s OpenSource
- MVC architecture allows for code separation
More information about CodeIgniter is available from CodeIgniter.com
CodeIgniter Base URL
When you install the CodeIgniter framework on your server, the base URL and certain other settings are automatically configured on install. These settings are relevant to the server you are installing on. The base url is set to the domain you are installing CodeIgniter on (eg. www.uk-webdeveloper.co.uk) and is called by a method in my class Start extends Controller in this manner:
function Start()
{
parent::Controller();
$this->load->helper('url');
$this->load->library('menu');
$this->load->library('menulower');
$this->load->library('banner');
$this->base = $this->config->item('base_url');
$this->css = $this->config->item('css');
}
As you can see from the method/function shown here, the base_url is located in the config file of your CodeIgniter installation.
Now, as mentioned above, CodeIgniter sets the base_url on install to that of the domain it is installed to. So what happens when you move the whole application to another domain? It may stop functioning.
The Base URL solution
The solution is quite simple.
1. Locate and open your config file (usually at system/application/config/config.php)
2. Find this line:
$config['base_url'] = ‘http://www.yourdomain.co.uk’
3. Replace that line with
$config['base_url'] = ‘http://’.$_SERVER['HTTP_HOST']
4. Save the file.
Now wherever you move the application to, it should still work as expected.
codeigniter base url
HTML5
Getting started with HTML5 is very easy.
HTML 5 is compatible with the XHTML syntax of self-closing tags, so, if you already use HTML5 then making the switch will be easy. Other XHTML features inherited by HTML5 include lowercase tags and double quoted attributes (eg, title=”the title”)
The Doctype declaration in HTML5 is so much easier to remember when compared to XHTML:
<!DOCTYPE html>
There’s a lot more to HTML5 and I will update this entry as I get more info.
