The section on extended functionality covers non-GUI classes that provide often needed application functions without a user interface. Some extended classes depend on core functionality, some contain independent classes.
Extended classes are treated differently from core classes in
that their code is not automatically included by
prepend.php3
. You have to include the class definition
manually where needed or you modify prepend.php3
.
The Cart class is programmatically independent, but makes sense
only if its instances are made persistent in some way. The Cart
class automatically registers itself as a session variable in
its start()
function.
Cart implements a shopping cart. At the moment, items within the shopping cart are independent of each other; the cart can only hold simple things. Support for compound articles that require other articles to function and provide a base for dependent articles is to be added at a future time.
An example of a simple article is any article with no options, for example an apple or a book. Common examples for compound articles are a pizza (which requires a foundation in either American or Italian style, a selection of toppings, and cheese, to function correctly) and a computer system (which requires a housing, a motherboard, RAM, a video card, etc to function correctly).
Note: Cart
was a core class up to release-5. If
your applications uses the Cart
class, you must
manually add the statement include("cart.inc")
to your
prepend.php3
file where indicated in that file.
Note: The page management functions do no longer support
the feature cart
to set up and start the cart class. It is
recommended that you use Session
's auto_init
feature
instead to start your cart automatically or that you manually
set up your cart.
classname | Serialization helper: The name of this class. |
persistent_slots | Serialization helper: The names of all persistent slots. |
item | Multidimensional array of items in the cart. |
currentItem | A counter for item positions. |
|
Checks that an item with the given article number $art
is
in the cart. Returns an array of a boolean value and an integer
number. If the boolean is true, there are number many articles
of that article number in the cart.
Deletes all items in current cart, resetting $this->currentItem to 1. Always returns true.
Returns the number of articles in the current shopping cart, or false if cart is empty.
Add $num
many articles of article number $art
to the current
shopping cart. Returns the position number of $art
in the
shopping cart.
Remove $num
many articles of article number $art
from the
shopping cart, if there are at least that many articles in the
cart. Returns the position number of $art
in the shopping cart
or false, if there weren't enough $art
to remove them from the
cart. If the function does return false, the cart has not been
modified.
Set the quantity of article number
Calls
This function should be provided by the user. It renders the
HTML to display a single item from the cart.
This function should be provided by the user. It renders the
prologue HTML to display a shopping cart listing.
This function should be provided by the user. It renders the
epilogue HTML to display a shopping cart listing.
Use a subclass of
$art
in the shopping cart to
exactly $num. If
Look up article numbers...
var $database_class = "DB_Article";
var $database_table = "articles";
var $db;
$num is set to zero, article is removed from
cart. Returns the position number of
$art
in the shopping cart.
show_item_open()
once at the beginning of a shopping
cart listing. Then calls show_item()
once for each item in
the shopping cart. Calls show_item_close()
once at the end
of a shopping cart listing.
$art
is the
article number of the item and there are $num
of these in
the cart.
Example
Cart
to provide an implementation of
show_item()
.
class My_Cart extends Cart {
var $classname = "My_Cart";
var $sum = 0;
function show_cart_open() { printf("<table class=cart_table>\n"); $this->sum = 0; }
function show_cart_close() { printf("</table>\n"); printf("That's a total of %s.\n", $this->sum); }
function show_item($art, $num) { if (!is_object($this->db)) { $class = $this->database_class; $this->db = new $class; }
$query = sprintf("select * from %s where artid = '%s'", $this->database_table, $art); $this->db->query($query);
while($this->db->next_record()) { printf(" <tr class=cart_row>\n <td class=cart_cell>%s</td>\n", $this->db->Record["name"]); printf(" <td class=cart_cell>%s</td>\n", $this->db->Record["price"]); printf(" <td class=cart_cell>%s</td>\n", $num); $rowsum = $num * $this->db->Record["price"]; $this->sum += $rowsum; printf(" <td class=cart_cell>%s</td>\n", $rowsum); printf(" </tr>\n"); } } }
To use a cart, create an instance of your Cart
subclass and
call start()
. This will automatically register cart
.
It is recommended that you set in your Session
subclass
in local.inc
the slot $auto_init
to the value
setup.inc
and create an include file of that name which
contains the following code:
global $cart; ## $cart is a global variable.
$cart = new My_Cart; ## Make a My_Cart instance named $cart
$cart->start(); ## and have it register itself.
Use add_item()
and remove_item
to work with your Cart:
$cart->add_item("101", 2); ## Add two pieces of "101"
$cart->remove_item("101", 1); ## Drop one piece of "101"
Use show_all()
to display the contents of your cart.
$cart->show_all(); ## What's in a cart, anyway?
To make use of the Cart class, you need to define a new table
in your database that lists all articles you shop should sell.
With PHPLIB and MySQL we recommend that you create a new
instance of PHPLIB for each virtual web server and a new database
for each customer. This database should hold the
active_sessions and auth_user tables as well as all
application specific tables like for example the article
list. In other words, with MySQL we strongly discourage
that you use PHPLIB and the MySQL directive use
database_name together. There is no support
if you do (there is no support if you do as we say, too,
because PHPLIB is an open source product you are using on your
own risk, but ...).
So let us assume you define a very simple new table articles
with a structure like this:
#
# Table structure for table 'articles'
#
CREATE TABLE articles (
name text,
price float(8,2),
artid int(11) DEFAULT '0' NOT NULL auto_increment,
PRIMARY KEY (artid)
);
This table has an article number called artid
, and for each
artid
there is an article description name
and a price
. You
may extend this minimal definition for your purposes by adding
article groups, BLOBs with article images and more, but this will
suffice for our example purposes.
Populate this table with some products that suit your taste.
The next step is to teach PHPLIB about the cart class. Three steps are necessary to do so:
Cart
class has to be included on every page. Even on
that pages that do not make use of the Cart
class.
On that pages that use Cart
, a cart subclass is instantiated and
saved. On all subsequent pages, that Cart
object is recreated and
to be able to recreate the Cart
object, PHP must know what a Cart
object is. Since you cannot know which pages a user loads after
he has put the first item into the Cart
, we need to have a
definition for Cart
on all pages.
The proper place to include the Cart
definition from cart.inc
is
consequently prepend.php3
. Edit prepend.php3
and
require("cart.inc")
as indicated by the comments in that file.
Cart
has to be created to suit your tastes.
Your subclass of Cart
will be called Example_Cart
in this example.
You may actually name it as you like, but you have to be
consistent.
The definition of Example_Cart
goes into local.inc
anywhere below
your definition for Example_Session
. It looks like this
class Example_Cart extends Cart {
var $classname = "Example_Cart";
}
and we will add additional code later in this example. That
additional code will teach your shopping cart about the database
table that holds your articles and so on.
auto_init
, after the instance variable of
Session that controls it.
Go into local.inc
and edit your subclass of Session
. You will
have some code like
class Example_Session extends Session {
var $classname = "Example_Session";
...
}
in your local.inc
. Add
a line like
var $auto_init = "setup.inc",
to your definition of Example_Session
and create a file
setup.inc
in the same directory that holds your local.inc.
Whatever code is in this file will be executed every time we
create a new session. The code is being executed after your
$sess
, $auth
and $perm
objects are loaded and
initialized, but does run from within a function context. You
have to global
everything you define to export it from that
function context.
In setup.inc
, create a global instance of
Example_Cart
named $cart
and register that variable
with PHPLIB:
<?php
global $cart;
$cart = new Example_Cart;
// $sess is already global
$sess->register("cart");
?>
Now you have a $cart
object available by default on every
page that uses PHPLIB. That object is created automatically at
session startup, is carried from page to page by PHPLIBs session
management and is destroyed by the garbage collection that reaps
session records. You do not have to worry anymore about that
cart, but simply use it anytime between page_open()
and page_close()
. PHPLIB does the rest for you.
The Cart
class is actually dead stupid. It maintains an array
$cart->item[]
that holds records about what the user bought. Each
$cart->item[$x]
consists of a
$cart->item[$x]["art"]
, which is
the article number of an item the user wants to buy and of a
$cart->item[$x]["num"]
, which is the # of items with that article
number that are wanted. $cart->currentItem
is the next $x to use
for articles added to $cart->item[]
.
You add articles to the shopping cart with
$x = $cart->add_item($art, $num)
This will add $num
items with the article number $art
to your cart contents. If you already have an item with that
article number in your cart, the count for that article is
increased by $num
. Otherwise a new article entry is being
created and set to $num
. The function does return the
$x
index into the $cart->item[]
array for that article.
To remove an item from the shopping cart, code
$x = $cart->remove_item($art, $num)
This will remove $num
items with the article number
$art
from your cart, if there are that many items in your
shopping cart. If you do not have the $art
in your cart or
there are not $num
many $art
in your cart, the
function will return false and not remove anything from the
cart. Otherwise, $num
articles with article number
$art
are taken out of the cart and if the count for that
article drops to zero while doing this, we even unset the array
element.
You may check how many articles with a given article number are in the cart:
list($have, $num) = $cart->check($art)
The check function does return a two-element array. The first
element $have
is true, if we have the wanted article in the cart.
If $have
is true, $num
holds the number of articles with that
number in the cart, otherwise $num
is undefined (actually, it is
0, but you must not rely on that).
Finally, we have a function
$cart->show_all()
which you may call to walk your shopping cart and have
Example_Cart to generate a list of articles in your cart. That
function will first call $cart->show_cart_open()
, for which you
may provide code in your subclass. It will then call
$cart->show_item($art, $num)
for each item in the cart. We have a
stupid default implementation for that function in Cart, but you
may provide more sophisticated code in Example_Cart
for that, too.
Finally, at the end of your cart listing,
$cart->show_cart_close()
is being called, which again may be code
of yours.
The example in the previous section shows a more
sophisticated implementation of a Cart subclass. That
implementation uses show_cart_open() to create an opening
table tag (formatted with a CSS class) and sets a counter
$cart->sum
to
zero.
In show_cart_close(), the table is being closed and the
$cart->sum
counter is printed.
As you might have guessed, show_item($art, $num)
queries the
database for each article number, retrieves the article
description and prices and finally sums up all prices, taking the
number of articles per article into consideration. It also
generates table rows, printing a nice receipt for the customer.