`validates_exclusion_of`¶

The validates_exclusion_of validation in ActiveRecord allows you to validate whether an attribute's value is excluded from a specified set of values. It is commonly used to ensure that an attribute does not have a value that falls within a predefined list or range. To use validates_exclusion_of, you need to specify the following options:

Attribute Name: This option specifies the name of the attribute you want to validate for exclusion. It is typically set as a symbol or string.
```
static $validates_exclusion_of = [
    'username' => []
];
```
In (Required): The in option defines the set of values that the attribute's value must be excluded from. It is required and should be set as an array of values to be excluded.
```
static $validates_exclusion_of = [
    'username' => [
        'in' => ['admin', 'root', 'superuser']
    ]
];
```

Message (Optional): To customize the error message displayed when the validation fails, you can use the message option to provide a custom error message.

static $validates_exclusion_of = [
    'status' => [
        'in' => ['blocked', 'banned'],
        'message' => 'Invalid status. Please choose a different status.',
    ],
];

Allow Blank (Optional): The allow_blank option allows you to specify whether the attribute is allowed to be empty (e.g., an empty string). By default, allow_blank is set to false, meaning that the attribute must not be blank. You can set it to true to allow blank values.
```
static $validates_exclusion_of = [
    'user_type' => [
        'in' => ['admin', 'moderator'], 
        'allow_blank' => true
    ]
];
```
Allow Null (Optional): The allow_null option allows you to specify whether the attribute is allowed to be null. By default, allow_nil is set to false, meaning that the attribute must not be null. You can set it to true to allow null values.
```
static $validates_exclusion_of = [
    'account_type' => [
        'in' => ['suspended', 'disabled'], 
        'allow_null' => true
    ]
];
```
On (Optional): The on option allows you to specify when the validation should occur. By default, it is set to 'save', which means the validation is performed when the record is saved. You can set it to 'create' to validate only during the creation of a new record or 'update' to validate only during updates.
```
static $validates_exclusion_of = [
    'user_role' => [
        'in' => ['admin', 'superuser'], 
        'on' => 'update'
    ]
];
```

Example of Usage:

```php class User extends ActiveRecord\Model { static $validates_exclusion_of = [ 'role' => [ 'in' => ['admin', 'superuser'], 'message' => 'Invalid role. Please choose a different role.', 'allow_blank' => true, ], ]; }

validates_exclusion_of¶

`validates_exclusion_of`¶