Building an Extensible Menu Class - I Say Method, You Say Madness... (
Page 5 of 10 )
With
the database design out of the way, it's now time to begin work on the methods
which will interact with the records in the database. Before actually sitting
down to code the class, it's a good idea to spend some time listing the
important methods, together with their purpose. Here's my initial
cut:
query($query) - execute an SQL query;
get_children($node) -
return a collection of this node's children;
get_parent($node) - return
the identifier of this node's parent;
get_label($node) - return the name
of this node
get_type($node) - return the node type (leaf or
branch)
is_root_node($node) - is this node at the root level or
not?
These are the essential methods; there may be more, which I will add
as development progresses.
Let's now begin by setting up the class
definition:
<?
// menu.class.php
// methods to obtain node and tree relationships
class Menu
{
}
?><hr noshade size=1 color=#cccccc></pre></blockquote>
Now, since this class will be talking to a database, I need to add a few
variables to hold database-specific information.
<blockquote><pre><hr noshade size=1 color=#cccccc><?
class Menu
{
// set up some variables with default values
// to hold database parameters
// hostname, user and password
var $hostname;
var $user;
var $pass;
// database and table containing menu data
var $db;
var $table;
}
?>
PHP makes it possible to automatically execute a specific
function when a new instance of a class is spawned. This function is referred to
as a "constructor" and must have the same name as the class.
In this
case, I plan to initialize my Menu object with certain default values for the
various database parameters. I have the option of assigning these variable-value
pairs individually, or writing a method to assign them all in one fell swoop; I
pick the latter.
<?
class Menu
{
// set up some variables
// snip
// constructor
function Menu()
{
$this->set_database_parameters("localhost", "me", "bs49h5634", "apps",
"menu");
}
// function: set database parameters
// returns: none
function set_database_parameters($hostname, $user, $password, $db, $table)
{
$this->hostname = $hostname;
$this->user = $user;
$this->password = $password;
$this->db = $db;
$this->table = $table;
}
}
?>
In case you're wondering, the $this prefix provides a
convenient way to access variables and functions which are "local" to the
class
Now, all the methods listed above will be querying the database for
information. Since the connect-and-query code is common to all of them, I can
extract it into a separate method named query().
<?
class Menu
{
// other methods
// function: execute query $query
// returns: result identifier
function query($query)
{
// connect
$connection = mysql_connect($this->hostname, $this->user, $this->pass) or
die ("Cannot connect to database");
// run query
$ret = mysql_db_query($this->db, $query, $connection) or die ("Error in
query: $query");
// return result identifier
return $ret;
}
}
?>
All my object methods can now simply use query() to execute
SQL queries on the database. Further - if I ever decide to move to another
database, I need only update the code in this single function to ensure that my
class will continue to work with the new system.{mospagebreak title=Playing With
Nodes} With the underlying, database-specific layer in place, I can now begin
work on the main object methods. The first of these is also one of the simplest
- it accepts a node id and returns the id of the node's parent.
<?
class Menu
{
// other methods
// function: get parent
// returns: node id
function get_parent($id)
{
$query = "SELECT parent FROM $this->table WHERE id = '$id'";
$result = $this->query($query);
$row = mysql_fetch_row($result);
return $row[0];
}
}
?>
An offshoot of this is the is_root_node() method, used to
test whether a particular node is at the base of the menu tree.
<?
class Menu
{
// other methods
// function: is this node at the root of the tree?
// returns: boolean
function is_root_node($id)
{
if($this->get_parent($id) == 0)
{
return 1;
}
else
{
return 0;
}
}
}
?>
The get_label() and get_link() methods accept a node id and
return the corresponding text and URL from the table.
<?
class Menu
{
// other methods
// function: get label for $id
// returns: string
function get_label($id)
{
$query = "SELECT label FROM $this->table WHERE id = '$id'";
$result = $this->query($query);
$row = mysql_fetch_row($result);
return $row[0];
}
// function: get link for $id
// returns: string
function get_link($id)
{
$query = "SELECT link FROM $this->table WHERE id = '$id'";
$result = $this->query($query);
$row = mysql_fetch_row($result);
return $row[0];
}
}
?>
Using the menu table constructed a few pages ago, the code
<?
$obj = new Menu();
echo $obj->get_label(3);
?>
would return
Los Angeles
/ 6 
