Handles saving only fields that have been changed in a record by the logged in user

save_diff.php

<?php
/**
 * SaveDiff component
 *
 * Handles saving only fields that have been changed in a record by the logged in user.
 *
 * @license http://www.opensource.org/licenses/mit-license.php The MIT License
 */
class SaveDiffComponent extends Object {
/**
 * Enabled flag.
 *
 * Prevents component from running unless certain criteria are met.
 *
 * @var boolean
 */
	public $enabled = null;
/**
 * Other components used.
 *
 * @var array
 */
	public $components = array(
		'Session', # This component relies on session storage.
	);
/**
 * Default options array.
 *
 * Contains an array of actions the component is enabled during.
 *
 * @var array
 * @todo Use in the real world and decide if other options are needed.
 */
	public $options = array(
		# list of controller action this component is enabled during
		'actions' => array(), # default: none
		# template for session path where original form data is stored (`String::insert`-compatible)
		'sessionKey' => 'SaveDiff.:modelClass.:modelId', # eg. 'SaveDiff.User.123'
	);
/**
 * Component initialize method.
 *
 * Called before `Controller::beforeFilter()`.
 *
 * @param object $controller Calling controller.
 * @param array $options Optional settings.
 * @return void
 */
	public function initialize(&$controller, $options = array()) {
		# merge in user defined options from controller level
		$this->options = array_merge($this->options, $options);
		# detect if controller should be enabled for this action.
		$this->enabled = in_array($controller->action, $this->options['actions']);
	}
/**
 * Component shotdown method.
 *
 * Called after `Controller::render()`. `$controller->data` should have outgoing data.
 *
 * @param object $controller Calling controller.
 * @return void
 */
	public function shutdown(&$controller) {
		# check component is enabled
		if (!$this->enabled) {
			return;
		}
		# check for validation failure (in case this is newly submitted data)
		$valid = empty($controller->{$controller->modelClass}->validationErrors);
		# generate a session key for record in data
		$sessionKey = $this->generateSessionKey($controller);
		# save form data to session if key was determined
		if ($valid && $sessionKey) {
			$originalData = $this->Session->write($sessionKey, $controller->data);
		}
	}
/**
 * Generate session key.
 *
 * @param object $controller Calling controller.
 * @return string Session key if record ID was determined, otherwise false.
 */
	public function generateSessionKey(&$controller) {
		# get primary model name
		$modelClass = $controller->modelClass;
		# controller has no models
		if (!$modelClass) {
			return false;
		}
		# get name of model's primary key field (default is `id`)
		$modelPrimaryKey = $controller->{$modelClass}->primaryKey;
		# check data and record id exists
		if (empty($controller->data[$modelClass][$modelPrimaryKey])) {
			return false;
		}
		# get the id of the model we are editing
		$modelId = $controller->data[$modelClass][$modelPrimaryKey];
		# create session storage key
		return String::insert($this->options['sessionKey'], compact('modelClass', 'modelId'));
	}
/**
 * Component startup method.
 *
 * Called after `Controller::beforeFilter()`, before action is called. `$controller->data` should have incoming data.
 *
 * @param object $controller Calling controller.
 * @param array $options Optional settings.
 * @return void
 */
	public function startup(&$controller) {
		# check component is enabled
		if (!$this->enabled) {
			return;
		}
		# generate a session key for record in data
		$sessionKey = $this->generateSessionKey($controller);
		# check if data has been submitted
		if ($sessionKey) {
			# get original stored data
			$originalData  = $this->Session->read($sessionKey);
			# get newly submitted data
			$submittedData = $controller->data;
			# extract all new changes
			$this->extractChanges($submittedData, $originalData);
		}
	}
/**
 * Compare two arrays and extract only changed data.
 *
 * @param array $newArray New data to remove unchanged data from.
 * @param array $oldArray Existing data.
 */
	public function extractChanges(&$newArray, &$oldArray) {
		# loop over array of new data
		foreach ($newArray as $key => $val) {
			# check item keys exist in other array before doing anything
			if (!array_key_exists($key, $oldArray)) {
				continue;
			}
			# if the value is an array, be recursive
			if (is_array($val)) {
				$this->extractChanges($newArray[$key], $oldArray[$key]);
			}
			# if the old data is the same as the new, delete the key/value pair
			if ($newArray[$key] == $oldArray[$key]) {
				unset($newArray[$key]);
			}
		}
	}
/**
 * Called before Controller::redirect().
 *
 * @param object $controller Controller with components to beforeRedirect
 * @return void
 */
	public function beforeRedirect(&$controller, $url, $status = null, $exit = true) {
		return true;
		# comment above line to prevent redirects and inspect data
		debug($controller->data);
		return false;
	}
}