document.ready() function is different from body onload() function for 2 reasons.
- We can have more than one document.ready() function in a page where we can have only one body onload function.
- document.ready() function is called as soon as DOM is loaded where body.onload() function is called when everything gets loaded on the page that includes DOM, images and all associated resources of the page.
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.
Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.
MySQLi is an improved version of the older PHP MySQL driver, offering various benefits.
The developers of the PHP programming language recommend using MySQLi when dealing with MySQL server versions 4.1.3 and newer
The MySQLi extension provides various benefits with respect to its predecessor, the most prominent of which are:
- An object-oriented interface
- Object Mapping
- Support for prepared statements
- Support for multiple statements
- Support for transactions
- Enhanced debugging support
- Embedded server support
- More powerful Functionality
phpMyAdmin is a free and open source tool written in PHP intended to handle the administration of MySQL with the use of a web browser. It can perform various tasks such as creating, modifying or deleting databases, tables, fields or rows; executing SQL statements; or managing users and permissions.
1) Execute sudo apt-get install phpmyadmin
2) Edit the file /etc/apache2/apache2.conf. and include the line Include /etc/phpmyadmin/apache.conf
3) Restart Apache sudo /etc/init.d/apache2 reload
- Web interface
- MySQL database management
- Import data from CSV and SQL
- Export data to various formats: CSV, SQL, XML, PDF (via the TCPDF library), ISO/IEC 26300 – OpenDocument Text and Spreadsheet, Word, Excel, LaTeX and others
- Administering multiple servers
- Creating PDF graphics of the database layout
- Creating complex queries using Query-by-Example (QBE)
- Searching globally in a database or a subset of it
- Transforming stored data into any format using a set of predefined functions, like displaying BLOB-data as image or download-link
- Live charts to monitor MySQL server activity like connections, processes, CPU/Memory usage, etc.
- Working with different operating systems.
Customer sessions stores data related to customer, checkout session stores data related to quote and order. They are actuall under one session in an array. So firstname in customer/session will be $_SESSION[‘customer’][‘firstname’] and cart items count in checkout/session will be $_SESSION[‘checkout’][‘items_count’]. The reason Magento uses session types separately is because once the order gets placed, the checkout session data information should get flushed which can be easily done by just unsetting $_SESSION[‘checkout’] session variable. So that the session is not cleared, just session data containing checkout information is cleared and rest all the session types are still intact.
The “magic” methods are ones with special names, starting with two underscores, which denote methods which will be triggered in response to particular PHP events. That might sound slightly automagical but actually it’s pretty straightforward, we already saw an example of this in the last post, where we used a constructor – so we’ll use this as our first example.
PHP functions that start with a double underscore – a “__” – are called magic functions (and/or methods) in PHP. They are functions that are always defined inside classes, and are not stand-alone (outside of classes) functions. The magic functions available in PHP are: __construct(), __destruct(), __call(), __callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __toString(), __invoke(), __set_state(), __clone(), and __autoload().
HTTP is a session less protocol. A connection is made to transfer a single file and closed once the transfer is complete. This keeps things simple but it’s not very efficient.
To improve efficiency something called KeepAlive was introduced. With KeepAlive the web browser and the web server agree to reuse the same connection to transfer multiple files.
Undefined value means the
- Variable used in the code doesn’t exist
- Variable is not assigned to any value
- Property doesn’t exist