Model.php

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

namespace yii\base;

use Yii;
use ArrayAccess;
use ArrayObject;
use ArrayIterator;
use ReflectionClass;
use IteratorAggregate;
use yii\helpers\ArrayHelper;
use yii\helpers\Inflector;
use yii\validators\RequiredValidator;
use yii\validators\Validator;
use yii\web\Link;
use yii\web\Linkable;

/**
 * Model is the base class for data models.
 *
 * Model implements the following commonly used features:
 *
 * - attribute declaration: by default, every public class member is considered as
 *   a model attribute
 * - attribute labels: each attribute may be associated with a label for display purpose
 * - massive attribute assignment
 * - scenario-based validation
 *
 * Model also raises the following events when performing data validation:
 *
 * - [[EVENT_BEFORE_VALIDATE]]: an event raised at the beginning of [[validate()]]
 * - [[EVENT_AFTER_VALIDATE]]: an event raised at the end of [[validate()]]
 *
 * You may directly use Model to store model data, or extend it with customization.
 * You may also customize Model by attaching [[ModelBehavior|model behaviors]].
 *
 * @property \yii\validators\Validator[] $activeValidators The validators applicable to the current
 * [[scenario]]. This property is read-only.
 * @property array $attributes Attribute values (name => value).
 * @property array $errors An array of errors for all attributes. Empty array is returned if no error. The
 * result is a two-dimensional array. See [[getErrors()]] for detailed description. This property is read-only.
 * @property array $firstErrors The first errors. An empty array will be returned if there is no error. This
 * property is read-only.
 * @property ArrayIterator $iterator An iterator for traversing the items in the list. This property is
 * read-only.
 * @property string $scenario The scenario that this model is in. Defaults to [[SCENARIO_DEFAULT]].
 * @property ArrayObject|\yii\validators\Validator[] $validators All the validators declared in the model.
 * This property is read-only.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class Model extends Component implements IteratorAggregate, ArrayAccess, Arrayable
{
	use ArrayableTrait;

	/**
	 * The name of the default scenario.
	 */
	const SCENARIO_DEFAULT = 'default';
	/**
	 * @event ModelEvent an event raised at the beginning of [[validate()]]. You may set
	 * [[ModelEvent::isValid]] to be false to stop the validation.
	 */
	const EVENT_BEFORE_VALIDATE = 'beforeValidate';
	/**
	 * @event Event an event raised at the end of [[validate()]]
	 */
	const EVENT_AFTER_VALIDATE = 'afterValidate';

	/**
	 * @var array validation errors (attribute name => array of errors)
	 */
	private $_errors;
	/**
	 * @var ArrayObject list of validators
	 */
	private $_validators;
	/**
	 * @var string current scenario
	 */
	private $_scenario = self::SCENARIO_DEFAULT;

	/**
	 * Returns the validation rules for attributes.
	 *
	 * Validation rules are used by [[validate()]] to check if attribute values are valid.
	 * Child classes may override this method to declare different validation rules.
	 *
	 * Each rule is an array with the following structure:
	 *
	 * ~~~
	 * [
	 *     ['attribute1', 'attribute2'],
	 *     'validator type',
	 *     'on' => ['scenario1', 'scenario2'],
	 *     ...other parameters...
	 * ]
	 * ~~~
	 *
	 * where
	 *
	 *  - attribute list: required, specifies the attributes array to be validated, for single attribute you can pass string;
	 *  - validator type: required, specifies the validator to be used. It can be a built-in validator name,
	 *    a method name of the model class, an anonymous function, or a validator class name.
	 *  - on: optional, specifies the [[scenario|scenarios]] array when the validation
	 *    rule can be applied. If this option is not set, the rule will apply to all scenarios.
	 *  - additional name-value pairs can be specified to initialize the corresponding validator properties.
	 *    Please refer to individual validator class API for possible properties.
	 *
	 * A validator can be either an object of a class extending [[Validator]], or a model class method
	 * (called *inline validator*) that has the following signature:
	 *
	 * ~~~
	 * // $params refers to validation parameters given in the rule
	 * function validatorName($attribute, $params)
	 * ~~~
	 *
	 * In the above `$attribute` refers to currently validated attribute name while `$params` contains an array of
	 * validator configuration options such as `max` in case of `string` validator. Currently validate attribute value
	 * can be accessed as `$this->[$attribute]`.
	 *
	 * Yii also provides a set of [[Validator::builtInValidators|built-in validators]].
	 * They each has an alias name which can be used when specifying a validation rule.
	 *
	 * Below are some examples:
	 *
	 * ~~~
	 * [
	 *     // built-in "required" validator
	 *     [['username', 'password'], 'required'],
	 *     // built-in "string" validator customized with "min" and "max" properties
	 *     ['username', 'string', 'min' => 3, 'max' => 12],
	 *     // built-in "compare" validator that is used in "register" scenario only
	 *     ['password', 'compare', 'compareAttribute' => 'password2', 'on' => 'register'],
	 *     // an inline validator defined via the "authenticate()" method in the model class
	 *     ['password', 'authenticate', 'on' => 'login'],
	 *     // a validator of class "DateRangeValidator"
	 *     ['dateRange', 'DateRangeValidator'],
	 * ];
	 * ~~~
	 *
	 * Note, in order to inherit rules defined in the parent class, a child class needs to
	 * merge the parent rules with child rules using functions such as `array_merge()`.
	 *
	 * @return array validation rules
	 * @see scenarios()
	 */
	public function rules()
	{
		return [];
	}

	/**
	 * Returns a list of scenarios and the corresponding active attributes.
	 * An active attribute is one that is subject to validation in the current scenario.
	 * The returned array should be in the following format:
	 *
	 * ~~~
	 * [
	 *     'scenario1' => ['attribute11', 'attribute12', ...],
	 *     'scenario2' => ['attribute21', 'attribute22', ...],
	 *     ...
	 * ]
	 * ~~~
	 *
	 * By default, an active attribute is considered safe and can be massively assigned.
	 * If an attribute should NOT be massively assigned (thus considered unsafe),
	 * please prefix the attribute with an exclamation character (e.g. '!rank').
	 *
	 * The default implementation of this method will return all scenarios found in the [[rules()]]
	 * declaration. A special scenario named [[SCENARIO_DEFAULT]] will contain all attributes
	 * found in the [[rules()]]. Each scenario will be associated with the attributes that
	 * are being validated by the validation rules that apply to the scenario.
	 *
	 * @return array a list of scenarios and the corresponding active attributes.
	 */
	public function scenarios()
	{
		$scenarios = [self::SCENARIO_DEFAULT => []];
		foreach ($this->getValidators() as $validator) {
			foreach ($validator->on as $scenario) {
				$scenarios[$scenario] = [];
			}
			foreach ($validator->except as $scenario) {
				$scenarios[$scenario] = [];
			}
		}
		$names = array_keys($scenarios);

		foreach ($this->getValidators() as $validator) {
			if (empty($validator->on) && empty($validator->except)) {
				foreach ($names as $name) {
					foreach ($validator->attributes as $attribute) {
						$scenarios[$name][$attribute] = true;
					}
				}
			} elseif (empty($validator->on)) {
				foreach ($names as $name) {
					if (!in_array($name, $validator->except, true)) {
						foreach ($validator->attributes as $attribute) {
							$scenarios[$name][$attribute] = true;
						}
					}
				}
			} else {
				foreach ($validator->on as $name) {
					foreach ($validator->attributes as $attribute) {
						$scenarios[$name][$attribute] = true;
					}
				}
			}
		}

		foreach ($scenarios as $scenario => $attributes) {
			if (empty($attributes) && $scenario !== self::SCENARIO_DEFAULT) {
				unset($scenarios[$scenario]);
			} else {
				$scenarios[$scenario] = array_keys($attributes);
			}
		}

		return $scenarios;
	}

	/**
	 * Returns the form name that this model class should use.
	 *
	 * The form name is mainly used by [[\yii\web\ActiveForm]] to determine how to name
	 * the input fields for the attributes in a model. If the form name is "A" and an attribute
	 * name is "b", then the corresponding input name would be "A[b]". If the form name is
	 * an empty string, then the input name would be "b".
	 *
	 * By default, this method returns the model class name (without the namespace part)
	 * as the form name. You may override it when the model is used in different forms.
	 *
	 * @return string the form name of this model class.
	 */
	public function formName()
	{
		$reflector = new ReflectionClass($this);
		return $reflector->getShortName();
	}

	/**
	 * Returns the list of attribute names.
	 * By default, this method returns all public non-static properties of the class.
	 * You may override this method to change the default behavior.
	 * @return array list of attribute names.
	 */
	public function attributes()
	{
		$class = new ReflectionClass($this);
		$names = [];
		foreach ($class->getProperties(\ReflectionProperty::IS_PUBLIC) as $property) {
			if (!$property->isStatic()) {
				$names[] = $property->getName();
			}
		}
		return $names;
	}

	/**
	 * Returns the attribute labels.
	 *
	 * Attribute labels are mainly used for display purpose. For example, given an attribute
	 * `firstName`, we can declare a label `First Name` which is more user-friendly and can
	 * be displayed to end users.
	 *
	 * By default an attribute label is generated using [[generateAttributeLabel()]].
	 * This method allows you to explicitly specify attribute labels.
	 *
	 * Note, in order to inherit labels defined in the parent class, a child class needs to
	 * merge the parent labels with child labels using functions such as `array_merge()`.
	 *
	 * @return array attribute labels (name => label)
	 * @see generateAttributeLabel()
	 */
	public function attributeLabels()
	{
		return [];
	}

	/**
	 * Performs the data validation.
	 *
	 * This method executes the validation rules applicable to the current [[scenario]].
	 * The following criteria are used to determine whether a rule is currently applicable:
	 *
	 * - the rule must be associated with the attributes relevant to the current scenario;
	 * - the rules must be effective for the current scenario.
	 *
	 * This method will call [[beforeValidate()]] and [[afterValidate()]] before and
	 * after the actual validation, respectively. If [[beforeValidate()]] returns false,
	 * the validation will be cancelled and [[afterValidate()]] will not be called.
	 *
	 * Errors found during the validation can be retrieved via [[getErrors()]],
	 * [[getFirstErrors()]] and [[getFirstError()]].
	 *
	 * @param array $attributes list of attributes that should be validated.
	 * If this parameter is empty, it means any attribute listed in the applicable
	 * validation rules should be validated.
	 * @param boolean $clearErrors whether to call [[clearErrors()]] before performing validation
	 * @return boolean whether the validation is successful without any error.
	 * @throws InvalidParamException if the current scenario is unknown.
	 */
	public function validate($attributes = null, $clearErrors = true)
	{
		$scenarios = $this->scenarios();
		$scenario = $this->getScenario();
		if (!isset($scenarios[$scenario])) {
			throw new InvalidParamException("Unknown scenario: $scenario");
		}

		if ($clearErrors) {
			$this->clearErrors();
		}
		if ($attributes === null) {
			$attributes = $this->activeAttributes();
		}
		if ($this->beforeValidate()) {
			foreach ($this->getActiveValidators() as $validator) {
				$validator->validateAttributes($this, $attributes);
			}
			$this->afterValidate();
			return !$this->hasErrors();
		}
		return false;
	}

	/**
	 * This method is invoked before validation starts.
	 * The default implementation raises a `beforeValidate` event.
	 * You may override this method to do preliminary checks before validation.
	 * Make sure the parent implementation is invoked so that the event can be raised.
	 * @return boolean whether the validation should be executed. Defaults to true.
	 * If false is returned, the validation will stop and the model is considered invalid.
	 */
	public function beforeValidate()
	{
		$event = new ModelEvent;
		$this->trigger(self::EVENT_BEFORE_VALIDATE, $event);
		return $event->isValid;
	}

	/**
	 * This method is invoked after validation ends.
	 * The default implementation raises an `afterValidate` event.
	 * You may override this method to do postprocessing after validation.
	 * Make sure the parent implementation is invoked so that the event can be raised.
	 */
	public function afterValidate()
	{
		$this->trigger(self::EVENT_AFTER_VALIDATE);
	}

	/**
	 * Returns all the validators declared in [[rules()]].
	 *
	 * This method differs from [[getActiveValidators()]] in that the latter
	 * only returns the validators applicable to the current [[scenario]].
	 *
	 * Because this method returns an ArrayObject object, you may
	 * manipulate it by inserting or removing validators (useful in model behaviors).
	 * For example,
	 *
	 * ~~~
	 * $model->validators[] = $newValidator;
	 * ~~~
	 *
	 * @return ArrayObject|\yii\validators\Validator[] all the validators declared in the model.
	 */
	public function getValidators()
	{
		if ($this->_validators === null) {
			$this->_validators = $this->createValidators();
		}
		return $this->_validators;
	}

	/**
	 * Returns the validators applicable to the current [[scenario]].
	 * @param string $attribute the name of the attribute whose applicable validators should be returned.
	 * If this is null, the validators for ALL attributes in the model will be returned.
	 * @return \yii\validators\Validator[] the validators applicable to the current [[scenario]].
	 */
	public function getActiveValidators($attribute = null)
	{
		$validators = [];
		$scenario = $this->getScenario();
		foreach ($this->getValidators() as $validator) {
			if ($validator->isActive($scenario) && ($attribute === null || in_array($attribute, $validator->attributes, true))) {
				$validators[] = $validator;
			}
		}
		return $validators;
	}

	/**
	 * Creates validator objects based on the validation rules specified in [[rules()]].
	 * Unlike [[getValidators()]], each time this method is called, a new list of validators will be returned.
	 * @return ArrayObject validators
	 * @throws InvalidConfigException if any validation rule configuration is invalid
	 */
	public function createValidators()
	{
		$validators = new ArrayObject;
		foreach ($this->rules() as $rule) {
			if ($rule instanceof Validator) {
				$validators->append($rule);
			} elseif (is_array($rule) && isset($rule[0], $rule[1])) { // attributes, validator type
				$validator = Validator::createValidator($rule[1], $this, (array) $rule[0], array_slice($rule, 2));
				$validators->append($validator);
			} else {
				throw new InvalidConfigException('Invalid validation rule: a rule must specify both attribute names and validator type.');
			}
		}
		return $validators;
	}

	/**
	 * Returns a value indicating whether the attribute is required.
	 * This is determined by checking if the attribute is associated with a
	 * [[\yii\validators\RequiredValidator|required]] validation rule in the
	 * current [[scenario]].
	 * @param string $attribute attribute name
	 * @return boolean whether the attribute is required
	 */
	public function isAttributeRequired($attribute)
	{
		foreach ($this->getActiveValidators($attribute) as $validator) {
			if ($validator instanceof RequiredValidator) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Returns a value indicating whether the attribute is safe for massive assignments.
	 * @param string $attribute attribute name
	 * @return boolean whether the attribute is safe for massive assignments
	 * @see safeAttributes()
	 */
	public function isAttributeSafe($attribute)
	{
		return in_array($attribute, $this->safeAttributes(), true);
	}

	/**
	 * Returns a value indicating whether the attribute is active in the current scenario.
	 * @param string $attribute attribute name
	 * @return boolean whether the attribute is active in the current scenario
	 * @see activeAttributes()
	 */
	public function isAttributeActive($attribute)
	{
		return in_array($attribute, $this->activeAttributes(), true);
	}

	/**
	 * Returns the text label for the specified attribute.
	 * @param string $attribute the attribute name
	 * @return string the attribute label
	 * @see generateAttributeLabel()
	 * @see attributeLabels()
	 */
	public function getAttributeLabel($attribute)
	{
		$labels = $this->attributeLabels();
		return isset($labels[$attribute]) ? $labels[$attribute] : $this->generateAttributeLabel($attribute);
	}

	/**
	 * Returns a value indicating whether there is any validation error.
	 * @param string|null $attribute attribute name. Use null to check all attributes.
	 * @return boolean whether there is any error.
	 */
	public function hasErrors($attribute = null)
	{
		return $attribute === null ? !empty($this->_errors) : isset($this->_errors[$attribute]);
	}

	/**
	 * Returns the errors for all attribute or a single attribute.
	 * @param string $attribute attribute name. Use null to retrieve errors for all attributes.
	 * @property array An array of errors for all attributes. Empty array is returned if no error.
	 * The result is a two-dimensional array. See [[getErrors()]] for detailed description.
	 * @return array errors for all attributes or the specified attribute. Empty array is returned if no error.
	 * Note that when returning errors for all attributes, the result is a two-dimensional array, like the following:
	 *
	 * ~~~
	 * [
	 *     'username' => [
	 *         'Username is required.',
	 *         'Username must contain only word characters.',
	 *     ],
	 *     'email' => [
	 *         'Email address is invalid.',
	 *     ]
	 * ]
	 * ~~~
	 *
	 * @see getFirstErrors()
	 * @see getFirstError()
	 */
	public function getErrors($attribute = null)
	{
		if ($attribute === null) {
			return $this->_errors === null ? [] : $this->_errors;
		} else {
			return isset($this->_errors[$attribute]) ? $this->_errors[$attribute] : [];
		}
	}

	/**
	 * Returns the first error of every attribute in the model.
	 * @return array the first errors. The array keys are the attribute names, and the array
	 * values are the corresponding error messages. An empty array will be returned if there is no error.
	 * @see getErrors()
	 * @see getFirstError()
	 */
	public function getFirstErrors()
	{
		if (empty($this->_errors)) {
			return [];
		} else {
			$errors = [];
			foreach ($this->_errors as $name => $es) {
				if (!empty($es)) {
					$errors[$name] = reset($es);
				}
			}
			return $errors;
		}
	}

	/**
	 * Returns the first error of the specified attribute.
	 * @param string $attribute attribute name.
	 * @return string the error message. Null is returned if no error.
	 * @see getErrors()
	 * @see getFirstErrors()
	 */
	public function getFirstError($attribute)
	{
		return isset($this->_errors[$attribute]) ? reset($this->_errors[$attribute]) : null;
	}

	/**
	 * Adds a new error to the specified attribute.
	 * @param string $attribute attribute name
	 * @param string $error new error message
	 */
	public function addError($attribute, $error = '')
	{
		$this->_errors[$attribute][] = $error;
	}

	/**
	 * Removes errors for all attributes or a single attribute.
	 * @param string $attribute attribute name. Use null to remove errors for all attribute.
	 */
	public function clearErrors($attribute = null)
	{
		if ($attribute === null) {
			$this->_errors = [];
		} else {
			unset($this->_errors[$attribute]);
		}
	}

	/**
	 * Generates a user friendly attribute label based on the give attribute name.
	 * This is done by replacing underscores, dashes and dots with blanks and
	 * changing the first letter of each word to upper case.
	 * For example, 'department_name' or 'DepartmentName' will generate 'Department Name'.
	 * @param string $name the column name
	 * @return string the attribute label
	 */
	public function generateAttributeLabel($name)
	{
		return Inflector::camel2words($name, true);
	}

	/**
	 * Returns attribute values.
	 * @param array $names list of attributes whose value needs to be returned.
	 * Defaults to null, meaning all attributes listed in [[attributes()]] will be returned.
	 * If it is an array, only the attributes in the array will be returned.
	 * @param array $except list of attributes whose value should NOT be returned.
	 * @return array attribute values (name => value).
	 */
	public function getAttributes($names = null, $except = [])
	{
		$values = [];
		if ($names === null) {
			$names = $this->attributes();
		}
		foreach ($names as $name) {
			$values[$name] = $this->$name;
		}
		foreach ($except as $name) {
			unset($values[$name]);
		}

		return $values;
	}

	/**
	 * Sets the attribute values in a massive way.
	 * @param array $values attribute values (name => value) to be assigned to the model.
	 * @param boolean $safeOnly whether the assignments should only be done to the safe attributes.
	 * A safe attribute is one that is associated with a validation rule in the current [[scenario]].
	 * @see safeAttributes()
	 * @see attributes()
	 */
	public function setAttributes($values, $safeOnly = true)
	{
		if (is_array($values)) {
			$attributes = array_flip($safeOnly ? $this->safeAttributes() : $this->attributes());
			foreach ($values as $name => $value) {
				if (isset($attributes[$name])) {
					$this->$name = $value;
				} elseif ($safeOnly) {
					$this->onUnsafeAttribute($name, $value);
				}
			}
		}
	}

	/**
	 * This method is invoked when an unsafe attribute is being massively assigned.
	 * The default implementation will log a warning message if YII_DEBUG is on.
	 * It does nothing otherwise.
	 * @param string $name the unsafe attribute name
	 * @param mixed $value the attribute value
	 */
	public function onUnsafeAttribute($name, $value)
	{
		if (YII_DEBUG) {
			Yii::trace("Failed to set unsafe attribute '$name' in '" . get_class($this) . "'.", __METHOD__);
		}
	}

	/**
	 * Returns the scenario that this model is used in.
	 *
	 * Scenario affects how validation is performed and which attributes can
	 * be massively assigned.
	 *
	 * @return string the scenario that this model is in. Defaults to [[SCENARIO_DEFAULT]].
	 */
	public function getScenario()
	{
		return $this->_scenario;
	}

	/**
	 * Sets the scenario for the model.
	 * Note that this method does not check if the scenario exists or not.
	 * The method [[validate()]] will perform this check.
	 * @param string $value the scenario that this model is in.
	 */
	public function setScenario($value)
	{
		$this->_scenario = $value;
	}

	/**
	 * Returns the attribute names that are safe to be massively assigned in the current scenario.
	 * @return string[] safe attribute names
	 */
	public function safeAttributes()
	{
		$scenario = $this->getScenario();
		$scenarios = $this->scenarios();
		if (!isset($scenarios[$scenario])) {
			return [];
		}
		$attributes = [];
		foreach ($scenarios[$scenario] as $attribute) {
			if ($attribute[0] !== '!') {
				$attributes[] = $attribute;
			}
		}
		return $attributes;
	}

	/**
	 * Returns the attribute names that are subject to validation in the current scenario.
	 * @return string[] safe attribute names
	 */
	public function activeAttributes()
	{
		$scenario = $this->getScenario();
		$scenarios = $this->scenarios();
		if (!isset($scenarios[$scenario])) {
			return [];
		}
		$attributes = $scenarios[$scenario];
		foreach ($attributes as $i => $attribute) {
			if ($attribute[0] === '!') {
				$attributes[$i] = substr($attribute, 1);
			}
		}
		return $attributes;
	}

	/**
	 * Populates the model with the data from end user.
	 * The data to be loaded is `$data[formName]`, where `formName` refers to the value of [[formName()]].
	 * If [[formName()]] is empty, the whole `$data` array will be used to populate the model.
	 * The data being populated is subject to the safety check by [[setAttributes()]].
	 * @param array $data the data array. This is usually `$_POST` or `$_GET`, but can also be any valid array
	 * supplied by end user.
	 * @param string $formName the form name to be used for loading the data into the model.
	 * If not set, [[formName()]] will be used.
	 * @return boolean whether the model is successfully populated with some data.
	 */
	public function load($data, $formName = null)
	{
		$scope = $formName === null ? $this->formName() : $formName;
		if ($scope == '' && !empty($data)) {
			$this->setAttributes($data);
			return true;
		} elseif (isset($data[$scope])) {
			$this->setAttributes($data[$scope]);
			return true;
		} else {
			return false;
		}
	}

	/**
	 * Populates a set of models with the data from end user.
	 * This method is mainly used to collect tabular data input.
	 * The data to be loaded for each model is `$data[formName][index]`, where `formName`
	 * refers to the value of [[formName()]], and `index` the index of the model in the `$models` array.
	 * If [[formName()]] is empty, `$data[index]` will be used to populate each model.
	 * The data being populated to each model is subject to the safety check by [[setAttributes()]].
	 * @param array $models the models to be populated. Note that all models should have the same class.
	 * @param array $data the data array. This is usually `$_POST` or `$_GET`, but can also be any valid array
	 * supplied by end user.
	 * @return boolean whether the model is successfully populated with some data.
	 */
	public static function loadMultiple($models, $data)
	{
		/** @var Model $model */
		$model = reset($models);
		if ($model === false) {
			return false;
		}
		$success = false;
		$scope = $model->formName();
		foreach ($models as $i => $model) {
			if ($scope == '') {
				if (isset($data[$i])) {
					$model->setAttributes($data[$i]);
					$success = true;
				}
			} elseif (isset($data[$scope][$i])) {
				$model->setAttributes($data[$scope][$i]);
				$success = true;
			}
		}
		return $success;
	}

	/**
	 * Validates multiple models.
	 * This method will validate every model. The models being validated may
	 * be of the same or different types.
	 * @param array $models the models to be validated
	 * @param array $attributes list of attributes that should be validated.
	 * If this parameter is empty, it means any attribute listed in the applicable
	 * validation rules should be validated.
	 * @return boolean whether all models are valid. False will be returned if one
	 * or multiple models have validation error.
	 */
	public static function validateMultiple($models, $attributes = null)
	{
		$valid = true;
		/** @var Model $model */
		foreach ($models as $model) {
			$valid = $model->validate($attributes) && $valid;
		}
		return $valid;
	}

	/**
	 * Returns the list of fields that should be returned by default by [[toArray()]] when no specific fields are specified.
	 *
	 * A field is a named element in the returned array by [[toArray()]].
	 *
	 * This method should return an array of field names or field definitions.
	 * If the former, the field name will be treated as an object property name whose value will be used
	 * as the field value. If the latter, the array key should be the field name while the array value should be
	 * the corresponding field definition which can be either an object property name or a PHP callable
	 * returning the corresponding field value. The signature of the callable should be:
	 *
	 * ```php
	 * function ($field, $model) {
	 *     // return field value
	 * }
	 * ```
	 *
	 * For example, the following code declares four fields:
	 *
	 * - `email`: the field name is the same as the property name `email`;
	 * - `firstName` and `lastName`: the field names are `firstName` and `lastName`, and their
	 *   values are obtained from the `first_name` and `last_name` properties;
	 * - `fullName`: the field name is `fullName`. Its value is obtained by concatenating `first_name`
	 *   and `last_name`.
	 *
	 * ```php
	 * return [
	 *     'email',
	 *     'firstName' => 'first_name',
	 *     'lastName' => 'last_name',
	 *     'fullName' => function () {
	 *         return $this->first_name . ' ' . $this->last_name;
	 *     },
	 * ];
	 * ```
	 *
	 * In this method, you may also want to return different lists of fields based on some context
	 * information. For example, depending on [[scenario]] or the privilege of the current application user,
	 * you may return different sets of visible fields or filter out some fields.
	 *
	 * The default implementation of this method returns [[attributes()]] indexed by the same attribute names.
	 *
	 * @return array the list of field names or field definitions.
	 * @see toArray()
	 */
	public function fields()
	{
		$fields = $this->attributes();
		return array_combine($fields, $fields);
	}

	/**
	 * Determines which fields can be returned by [[toArray()]].
	 * This method will check the requested fields against those declared in [[fields()]] and [[extraFields()]]
	 * to determine which fields can be returned.
	 * @param array $fields the fields being requested for exporting
	 * @param array $expand the additional fields being requested for exporting
	 * @return array the list of fields to be exported. The array keys are the field names, and the array values
	 * are the corresponding object property names or PHP callables returning the field values.
	 */
	protected function resolveFields(array $fields, array $expand)
	{
		$result = [];

		foreach ($this->fields() as $field => $definition) {
			if (is_integer($field)) {
				$field = $definition;
			}
			if (empty($fields) || in_array($field, $fields, true)) {
				$result[$field] = $definition;
			}
		}

		if (empty($expand)) {
			return $result;
		}

		foreach ($this->extraFields() as $field => $definition) {
			if (is_integer($field)) {
				$field = $definition;
			}
			if (in_array($field, $expand, true)) {
				$result[$field] = $definition;
			}
		}

		return $result;
	}

	/**
	 * Returns an iterator for traversing the attributes in the model.
	 * This method is required by the interface IteratorAggregate.
	 * @return ArrayIterator an iterator for traversing the items in the list.
	 */
	public function getIterator()
	{
		$attributes = $this->getAttributes();
		return new ArrayIterator($attributes);
	}

	/**
	 * Returns whether there is an element at the specified offset.
	 * This method is required by the SPL interface `ArrayAccess`.
	 * It is implicitly called when you use something like `isset($model[$offset])`.
	 * @param mixed $offset the offset to check on
	 * @return boolean
	 */
	public function offsetExists($offset)
	{
		return $this->$offset !== null;
	}

	/**
	 * Returns the element at the specified offset.
	 * This method is required by the SPL interface `ArrayAccess`.
	 * It is implicitly called when you use something like `$value = $model[$offset];`.
	 * @param mixed $offset the offset to retrieve element.
	 * @return mixed the element at the offset, null if no element is found at the offset
	 */
	public function offsetGet($offset)
	{
		return $this->$offset;
	}

	/**
	 * Sets the element at the specified offset.
	 * This method is required by the SPL interface `ArrayAccess`.
	 * It is implicitly called when you use something like `$model[$offset] = $item;`.
	 * @param integer $offset the offset to set element
	 * @param mixed $item the element value
	 */
	public function offsetSet($offset, $item)
	{
		$this->$offset = $item;
	}

	/**
	 * Sets the element value at the specified offset to null.
	 * This method is required by the SPL interface `ArrayAccess`.
	 * It is implicitly called when you use something like `unset($model[$offset])`.
	 * @param mixed $offset the offset to unset element
	 */
	public function offsetUnset($offset)
	{
		$this->$offset = null;
	}
}