Question

I am new to php and currently I am reading Wrox Professional PHP 5.

Can anyone explain me the following code ?

<? php

abstract class PropertyObject
{
//Stores name/value pairs that hook properties to database field names
protected $propertyTable=array();

//List of properties that have been modified.
protected $changedProperties=array();

//Actual data from the database.
protected $data;

//Any validation errors that might have occured.
protected $errors=array();

public function __construct($arData)
{
     $this->data=$arData;
}

function __get($propertyName)
{
     if(!array_key_exits($propertyName,$this->propertyTable))
     {
          throw new Exception("Invalid property \"$propertyName\" !");
     }

     if(method_exists($this,'get'.$propertyName))
     {
          return call_user_func(array($this,'get'.$propertyName));
     }
     else
     {
          return $this->data[$this->propertyTable[$propertyName]];
     }
}

function __set($propertyName,$value)
{
     if(!array_key_exits($propertyName,$this->propertyTable))
     {
          throw new Exception("Invalid property \"$propertyName\" !")
     }

     if(method_exits($this,'set'.$propertyName))
     {
     return call_user_func(array($this,'set'.$propertyName),$value);
     }
     else
     {
     //If the value of the property really has changed and it's not already in the changedProperties array, add it.

          if($this->propertyTable[$propertyName] !=$value && !in_array($propertyName,$this->changedProperties))
          {
               $this->changedProperties[]=$propertyName;
          }

          //Now set the new value
          $this->data[$this->propertyTable[$propertyName]]=$value;

     }
}

}
?>

I can’t understand the code inside assessor get and set methods.

Answer 1

The __get magic method is called when a property of the object is requested but it wasn’t declared or specifically assigned (for dynamic properties). This implementation:

• First tries to see if the logical property exists as an entry in the actual declared property named $propertyTable.
• If it doesn’t exist, it throws an exception, therefore leaving the method,
• If it exists and additionaly exists a method named 'get'.$propertyName (i.e., "get" concatenated with the request property name), that method is called and its value is returned.
• If it exists but there’s no such method, it returns the value of the entry with key $propertyName in the declared property $propertyTable.

Given this, I think you can figure __set out. See Magic Methods in the PHP manual.