www.mikescher.com/framework/validators/CExistValidator.php

<?php
/**
 * CExistValidator class file.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright 2008-2013 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * CExistValidator validates that the attribute value exists in a table.
 *
 * This validator is often used to verify that a foreign key contains a value
 * that can be found in the foreign table.
 *
 * When using the {@link message} property to define a custom error message, the message
 * may contain additional placeholders that will be replaced with the actual content. In addition
 * to the "{attribute}" placeholder, recognized by all validators (see {@link CValidator}),
 * CExistValidator allows for the following placeholders to be specified:
 * <ul>
 * <li>{value}: replaced with value of the attribute.</li>
 * </ul>
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @package system.validators
 */
class CExistValidator extends CValidator
{
	/**
	 * @var boolean whether the comparison is case sensitive. Defaults to true.
	 * Note, by setting it to false, you are assuming the attribute type is string.
	 */
	public $caseSensitive=true;
	/**
	 * @var string the ActiveRecord class name that should be used to
	 * look for the attribute value being validated. Defaults to null,
	 * meaning using the ActiveRecord class of the attribute being validated.
	 * You may use path alias to reference a class name here.
	 * @see attributeName
	 */
	public $className;
	/**
	 * @var string the ActiveRecord class attribute name that should be
	 * used to look for the attribute value being validated. Defaults to null,
	 * meaning using the name of the attribute being validated.
	 * @see className
	 */
	public $attributeName;
	/**
	 * @var mixed additional query criteria. Either an array or CDbCriteria.
	 * This will be combined with the condition that checks if the attribute
	 * value exists in the corresponding table column.
	 * This array will be used to instantiate a {@link CDbCriteria} object.
	 */
	public $criteria=array();
	/**
	 * @var boolean whether the attribute value can be null or empty. Defaults to true,
	 * meaning that if the attribute is empty, it is considered valid.
	 */
	public $allowEmpty=true;

	/**
	 * Validates the attribute of the object.
	 * If there is any error, the error message is added to the object.
	 * @param CModel $object the object being validated
	 * @param string $attribute the attribute being validated
	 * @throws CException if given table does not have specified column name
	 */
	protected function validateAttribute($object,$attribute)
	{
		$value=$object->$attribute;
		if($this->allowEmpty && $this->isEmpty($value))
			return;

		if(is_array($value))
		{
			// https://github.com/yiisoft/yii/issues/1955
			$this->addError($object,$attribute,Yii::t('yii','{attribute} is invalid.'));
			return;
		}

		$className=$this->className===null?get_class($object):Yii::import($this->className);
		$attributeName=$this->attributeName===null?$attribute:$this->attributeName;
		$finder=$this->getModel($className);
		$table=$finder->getTableSchema();
		if(($column=$table->getColumn($attributeName))===null)
			throw new CException(Yii::t('yii','Table "{table}" does not have a column named "{column}".',
				array('{column}'=>$attributeName,'{table}'=>$table->name)));

		$columnName=$column->rawName;
		$criteria=new CDbCriteria();
		if($this->criteria!==array())
			$criteria->mergeWith($this->criteria);
		$tableAlias = empty($criteria->alias) ? $finder->getTableAlias(true) : $criteria->alias;
		$valueParamName = CDbCriteria::PARAM_PREFIX.CDbCriteria::$paramCount++;
		$criteria->addCondition($this->caseSensitive ? "{$tableAlias}.{$columnName}={$valueParamName}" : "LOWER({$tableAlias}.{$columnName})=LOWER({$valueParamName})");
		$criteria->params[$valueParamName] = $value;

		if(!$finder->exists($criteria))
		{
			$message=$this->message!==null?$this->message:Yii::t('yii','{attribute} "{value}" is invalid.');
			$this->addError($object,$attribute,$message,array('{value}'=>CHtml::encode($value)));
		}
	}

	/**
	 * Given active record class name returns new model instance.
	 *
	 * @param string $className active record class name.
	 * @return CActiveRecord active record model instance.
	 *
	 * @since 1.1.14
	 */
	protected function getModel($className)
	{
		return CActiveRecord::model($className);
	}
}