Yii form model that allows for using multiple models in the same form.

ModelGroupForm.php

<?php

/**
 * Class ModelGroupForm
 * 
 * Note! Attributes must be defined as "modelName.attributeName", e.g. "user.name" in forms.
 */
class ModelGroupForm extends CFormModel {
	/**
	 * @var CModel[] $models the model instances (name=>config).
	 */
	public $models = array();

	/**
	 * Does magic for getting attributes within in group models.
	 * @param string $name the property name or event name
	 * @return mixed the property value, event handlers attached to the event, or the named behavior
	 * @throws CException if the property or event is not defined
	 */
	public function __get($name) {
		$name = $this->resolveModelAttribute($name);
		if (is_array($name)) {
			list($modelName, $attribute) = $name;
			if (!empty($attribute) && isset($this->models[$modelName])) {
				return $this->models[$modelName]->{$attribute};
			}
		}
		return parent::__get($name);
	}

	/**
	 * Sets the attribute values in a massive way.
	 * @param array $values attribute values (name=>value) to be set.
	 * @param boolean $safeOnly whether the assignments should only be done to the safe attributes.
	 */
	public function setAttributes($values, $safeOnly = true) {
		parent::setAttributes($values, $safeOnly);
		foreach ($values as $name => $value) {
			$name = $this->resolveModelAttribute($name);
			if (is_array($name)) {
				list($name, $attribute) = $name;
				if (isset($this->models[$name])) {
					$this->models[$name]->{$attribute} = $value;
				}
			}
		}
	}

	/**
	 * Performs the validation.
	 * @param array $attributes list of attributes that should be validated. Defaults to null,
	 * @param boolean $clearErrors whether to call {@link clearErrors} before performing validation
	 * @return boolean whether the validation is successful without any error.
	 */
	public function validate($attributes = null, $clearErrors = true) {
		$valid = parent::validate($attributes, $clearErrors);
		foreach ($this->models as $model) {
			$valid = $model->validate(null, $clearErrors) && $valid;
		}
		return $valid;
	}

	/**
	 * Returns the text label for the specified attribute.
	 * @param string $attribute the attribute name
	 * @return string the attribute label
	 */
	public function getAttributeLabel($attribute) {
		$attribute = $this->resolveModelAttribute($attribute);
		if (is_array($attribute)) {
			list($modelName, $attributeName) = $attribute;
			if (!empty($attributeName) && isset($this->models[$modelName])) {
				return $this->models[$modelName]->getAttributeLabel($attributeName);
			}
			return '';
		} else {
			return parent::getAttributeLabel($attribute);
		}
	}

	/**
	 * Returns a value indicating whether there is any validation error.
	 * @param string $attribute attribute name. Use null to check all attributes.
	 * @return boolean whether there is any error.
	 */
	public function hasErrors($attribute = null) {
		$attribute = $this->resolveModelAttribute($attribute);
		if (is_array($attribute)) {
			list($modelName, $attributeName) = $attribute;
			if (isset($this->models[$modelName])) {
				return $this->models[$modelName]->hasErrors($attributeName);
			}
		}
		return parent::hasErrors($attribute);
	}

	/**
	 * Returns the errors for all attribute or a single attribute.
	 * @param string $attribute attribute name. Use null to retrieve errors for all attributes.
	 * @return array errors for all attributes or the specified attribute. Empty array is returned if no error.
	 */
	public function getErrors($attribute = null) {
		$errors = parent::getErrors($attribute);
		foreach ($this->models as $model) {
			$errors = array_merge($errors, $model->getErrors($attribute));
		}
		return $errors;
	}

	/**
	 * Returns the first error of the specified attribute.
	 * @param string $attribute attribute name.
	 * @return string the error message. Null is returned if no error.
	 */
	public function getError($attribute) {
		$attribute = $this->resolveModelAttribute($attribute);
		if (is_array($attribute)) {
			list($modelName, $attribute) = $attribute;
			if (!empty($attribute) && isset($this->models[$modelName])) {
				return $this->models[$modelName]->getError($attribute);
			}
			return '';
		}
		return parent::getError($attribute);
	}

	/**
	 * Turns model.attribute into array($model, $attribute)
	 * @param $attribute
	 * @return array
	 */
	public function resolveModelAttribute($attribute) {
		return strpos($attribute, '.') > 0 ? explode('.', $attribute) : $attribute;
	}
}