Model
=====

A model in Yii is intended for application data storage and has the following basic features:

- attribute declaration: a model defines what is considered an attribute.
- attribute labels: each attribute may be associated with a label for display purpose.
- massive attribute assignment.
- scenario-based data validation.

Models extending from [[\yii\base\Model]] class are typically used to hold data and corresponding validation rules of complex web forms.
The class is also a base for more advanced models with additional functionality such as [Active Record](active-record.md).

Attributes
----------

Attributes store the actual data represented by a model and can
be accessed like object member variables. For example, a `Post` model
may contain a `title` attribute and a `content` attribute which may be
accessed as follows:

```php
$post = new Post;
$post->title = 'Hello, world';
$post->content = 'Something interesting is happening';
echo $post->title;
echo $post->content;
```

Since model implements [ArrayAccess](http://php.net/manual/en/class.arrayaccess.php) interface you can use it
as if it was an array:

```php
$post = new Post;
$post['title'] = 'Hello, world';
$post['content'] = 'Something interesting is happening';
echo $post['title'];
echo $post['content'];
```

Default model implementation has a strict rule that all its attributes should be explicitly declared as public and
non-static class properties such as the following:

```php
// LoginForm has two attributes: username and password
class LoginForm extends \yii\base\Model
{
	public $username;
	public $password;
}
```

In order to change this, you can override `attributes()` method that returns a list of model attribute names.


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 for example as a form label.

By default an attribute label is generated using [[\yii\base\Model\generateAttributeLabel()]] but the better way is to
specify it explicitly like the following:

```php
// LoginForm has two attributes: username and password
class LoginForm extends \yii\base\Model
{
	public $username;
	public $password;

	public function attributeLabels()
	{
		reuturn array(
			'username' => 'Your name',
			'password' => 'Your password',
		);
	}
}
```

Scenarios
---------

A model may be used in different scenarios. For example, a `User` model may be used to collect user login inputs,
and it may also be used for user registration purpose. For this reason, each model has a property named `scenario`
which stores the name of the scenario that the model is currently being used in. As we will explain in the next
few sections, the concept of scenario is mainly used for validation and massive attribute assignment.

Associated with each scenario is a list of attributes that are *active* in that particular scenario. For example,
in the `login` scenario, only the `username` and `password` attributes are active; while in the `register` scenario,
additional attributes such as `email` are *active*.

Possible scenarios should be listed in the `scenarios()` method which returns an array whose keys are the scenario
names and whose values are the corresponding active attribute lists. Below is an example:

```php
class User extends \yii\db\ActiveRecord
{
	public function scenarios()
	{
		return array(
			'login' => array('username', 'password'),
			'register' => array('username', 'email', 'password'),
		);
	}
}
```

Sometimes, we want to mark an attribute as not safe for massive assignment (but we still want it to be validated).
We may do so by prefixing an exclamation character to the attribute name when declaring it in `scenarios()`. For example,

```php
array('username', 'password', '!secret')
```

Validation
----------

When a model is used to collect user input data via its attributes, it usually needs to validate the affected attributes
to make sure they satisfy certain requirements, such as an attribute cannot be empty, an attribute must contain letters
only, etc. If errors are found in validation, they may be presented to the user to help him fix the errors.
The following example shows how the validation is performed:

```php
$model = new LoginForm;
$model->username = $_POST['username'];
$model->password = $_POST['password'];
if ($model->validate()) {
	// ... login the user ...
} else {
	$errors = $model->getErrors();
	// ... display the errors to the end user ...
}
```

The possible validation rules for a model should be listed in its `rules()` method. Each validation rule applies to one
or several attributes and is effective in one or several scenarios. A rule can be specified using a validator object - an
instance of a [[\yii\validators\Validator]] child class, or an array with the following format:

```php
array(
	'attribute1, attribute2, ...',
	'validator class or alias',
	// specifies in which scenario(s) this rule is active.
	// if not given, it means it is active in all scenarios
	'on' => 'scenario1, scenario2, ...',
	// the following name-value pairs will be used
	// to initialize the validator properties
	'property1' => 'value1',
	'property2' => 'value2',
	// ...
)
```

When `validate()` is called, the actual validation rules executed are determined using both of the following criteria:

- the rule must be associated with at least one active attribute;
- the rule must be active for the current scenario.


### Active Attributes

An attribute is *active* if it is subject to some validations in the current scenario.


### Safe Attributes

An attribute is *safe* if it can be massively assigned in the current scenario.


Massive Attribute Retrieval and Assignment
------------------------------------------

Attributes can be massively retrieved via the `attributes` property.
The following code will return *all* attributes in the `$post` model
as an array of name-value pairs.

```php
$attributes = $post->attributes;
var_dump($attributes);
```

Using the same `attributes` property you can massively assign data from associative array to model attributes:

```php
$attributes = array(
	'title' => 'Model attributes',
	'create_time' => time(),
);
$post->attributes = $attributes;
```

In the code above we're assigning corresponding data to model attributes named as array keys. The key difference from mass
retrieval that always works for all attributes is that in order to be assigned an attribute should be **safe** else
it will be ignored.


Validation rules and mass assignment
------------------------------------

In Yii2 unlike Yii 1.x validation rules are separated from mass assignment. Validation
rules are described in `rules()` method of the model while what's safe for mass
assignment is described in `scenarios` method:

```php
function rules()
{
	return array(
		// rule applied when corresponding field is "safe"
		array('username', 'length', 'min' => 2),
		array('first_name', 'length', 'min' => 2),
		array('password', 'required'),

		// rule applied when scenario is "signup" no matter if field is "safe" or not
		array('hashcode', 'check', 'on' => 'signup'),
	);
}

function scenarios()
{
	return array(
		// on signup allow mass assignment of username
		'signup' => array('username', 'password'),
		'update' => array('username', 'first_name'),
	);
}
```

Note that everything is unsafe by default and you can't make field "safe" without specifying scenario.


See also
--------

- [Model validation reference](validation.md)
- [[\yii\base\Model]]