gistfile1.php

<?php
class Entity
{
    protected $_ruleSet;
    
    public function __construct([..], RuleSet $ruleSet = null)
    {
        $this->_ruleSet = $ruleSet
    }
    
    public function validate()
    {
        return $this->_ruleSet->brokenBy($this);
    }
    
    public function setRuleSet(RuleSet $ruleSet)
    {
        $this->_ruleSet = $ruleSet;
    }
    
    public function getRuleSet()
    {
        return $this->_ruleSet;
    }
}

class RuleSet
{
    protected $_rules = array();
    
    public function __construct(array $rules = array())
    {
        $this->setRules($rules);
    }
    
    public function setRules(array $rules)
    {
        foreach ($rules as $key => $keyRules) {
            foreach ($keyRules as $rule) {
                $this->addRule($key, $rule);
            }
        }
    }
    
    public function addRule($key, \Zend_Validate_Interface $validator)
    {
        $this->_rules[$key] = $validator;
    }
    
    public function getRules($key = null)
    {
        if (null === $key) {
            return $this->_keys;
        }
        
        if (!isset($this->_rules[$keys])) {
            throw new \Exception('Rule key is not valid');
        }
        
        return $this->_rules[$keys];
    }
    
    public function brokenBy(Entity $entity)
    {
        $this->_messages = array();
        
        foreach ($this->getRules() as $key => $rules) {
            $accessor = 'get' . $key;
            if (!is_callable(array($entity, $accessor))) {
                continue;
            }
            
            if (!$rules->isValid($entity->$accessor())) {
                $this->_messages[$key] = $rules->getMessages();
            }
        }
        
        return (bool) count($this->_messages);
    }
}

class EntityFormValidator implements \Zend_Validate_Interface
{
    protected $_rule;
    
    public function __construct($entity, $property)
    {
        $this->_entity = $entity;
        $this->_rule = $entity->getRuleSet()->getRules($property);
    }
    
    public function isValid($value)
    {
        return $this->_rule->isValid($value);
    }
    
    public function getMessages()
    {
        return $this->_rule->getMessages();
    }
}

// implementation:
$form->getElement('foo')->addValidator(new EntityFormValidator($entity, 'foo'));