<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\caching;

use Yii;
use yii\base\InvalidConfigException;
use yii\db\Connection;

/**
 * DbDependency represents a dependency based on the query result of a SQL statement.
 *
 * If the query result changes, the dependency is considered as changed.
 * The query is specified via the [[sql]] property.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class DbDependency extends Dependency
{
	/**
	 * @var string the application component ID of the DB connection.
	 */
	public $db = 'db';
	/**
	 * @var string the SQL query whose result is used to determine if the dependency has been changed.
	 * Only the first row of the query result will be used. This property must be always set, otherwise
	 * an exception would be raised.
	 */
	public $sql;
	/**
	 * @var array the parameters (name=>value) to be bound to the SQL statement specified by [[sql]].
	 */
	public $params = array();

	/**
	 * Initializes the database dependency object.
	 */
	public function init()
	{
		if ($this->sql === null) {
			throw new InvalidConfigException('DbDependency::sql must be set.');
		}
	}

	/**
	 * Generates the data needed to determine if dependency has been changed.
	 * This method returns the value of the global state.
	 * @return mixed the data needed to determine if dependency has been changed.
	 */
	protected function generateDependencyData()
	{
		$db = Yii::$app->getComponent($this->db);
		if (!$db instanceof Connection) {
			throw new InvalidConfigException("DbDependency::db must be the application component ID of a DB connection.");
		}

		if ($db->enableQueryCache) {
			// temporarily disable and re-enable query caching
			$db->enableQueryCache = false;
			$result = $db->createCommand($this->sql, $this->params)->queryRow();
			$db->enableQueryCache = true;
		} else {
			$result = $db->createCommand($this->sql, $this->params)->queryRow();
		}
		return $result;
	}
}