在数据库中使用对象有那些好处？ (2)

这类方法被转移到被称作记录（Record）的抽象的超级类（super class），当然它是User类下的子类
这个记录类（Record class）掌握所有存取数组 $_data的细节，在内容被修改之前调用验证的方法，以及将变更的通知发给记录（Records），就像发给中心对象存储（ObjectStore）实例。
 
<?php
class User extends Record {

  // --- OMITTED CODE --- //

  /**
  * Do not show the actual password for the user, only some asterixes with the same strlen as the password value.
  */
  function password() {
       $passLength = strlen( $this->_getData('password'));
      return str_repeat('*',  $passLength);
  }
  /**
  * Setting the user password is not affected.
  */
  function setPassword( $newPassword) {
       $this->_setData('password',  $newPassword);
  }

  /**
  * fullName is a derived attribute from firstName and lastName
  * and does not need to be stored as a variable.
  * It is therefore read-only, and has no 'setFullname()' accessor method.
  */
  function fullName() {
      return  $this->firstName() . " " .  $this->lastName();
  }

  /**
  * Spending limit returns the currency value of the user's spending limit.
  * This value is stored as an INT in the database, eliminating the need
  * for more expensive DECIMAL or DOUBLE column types.
  */
  function spendingLimit() {
      return  $this->_getData('spendingLimit') / 100;
  }

  /**
  * The set accessor multiplies the currency value by 100, so it can be stored in the database again
  * as an INT value.
  */
  function setSpendingLimit( $newSpendLimit) {
       $this->_setData('spendingLimit',  $newSpendLimit * 100);
  }

  /**
  * The validateSpendingLimit is not called in this class, but is called automatically by the _setData() method
  * in the Record superclass, which in turn is called by the setSpendingLimit() method.
  */
  function validateSpendingLimit(& $someLimit) {
      if (is_numeric( $someLimit) AND  $someLimit >= 0) {
          return true;
      } else {
          throw new Exception("Spending limit must be a non-negative integer"); //PHP5 only
      }
  }
}

/**
* Record is the superclass for all database objects.
*/
abstract class Record {
  var  $_data = array();
  var  $_modifiedKeys = array(); // keeps track of which fields have changed since record was created/fetched

  /**
  * Returns an element from the  $_data associative array.
  */
  function _getData( $attributeName) {
      return  $this->_data[ $attributeName];
  }

  /**
  * If the supplied value passes validation, this
  * sets the value in the  $_data associative array.
  */
  function _setData( $attributeName,  $value) {
      if ( $this->validateAttribute( $attributeName,  $value)) {
          if ( $value !=  $this->_data[ $attributeName]) {
               $this->_data[ $attributeName] =  $value;
               $this->_modifiedKeys[] =  $attributeName;
               $this->didChange();
          } else {
              // the new value is identical to the current one
              // no change necessary
          }
      }
  }

  /**
  * For an attribute named "foo", this looks for a method named "validateFoo()"
  * and calls it if it exists.  Otherwise this returns true (meaning validation passed).
  */
  function validateAttribute( $attributeName, & $value) {
       $methodName = 'validate' .  $attributeName;
      if (method_exists( $this,  $methodName)) {
          return  $this-> $methodName( $value);
      } else {
          return true;
      }
  }

  function didChange() {
      // notify the objectStore that this record changed
  }
}
?>