- Validation
- Available Validation Rules
- accepted
- active_url
- after:date
- alpha
- alpha_dash
- alpha_num
- array
- before:date
- between:min,max
- boolean
- confirmed
- date
- date_format:format
- different:field
- digits:value
- digits_between:min,max
- dimensions
- distinct
- exists:table,column
- Basic Usage Of Exists Rule
- Specifying A Custom Column Name
- file
- filled
- image
- in:foo,bar,…
- in_array:anotherfield
- integer
- ip
- json
- max:value
- mimetypes:text/plain,…
- mimes:foo,bar,…
- Basic Usage Of MIME Rule
- min:value
- not_in:foo,bar,…
- numeric
- present
- regex:pattern
- required
- required_if:anotherfield,value,…
- required_unless:anotherfield,value,…
- required_with:foo,bar,…
- required_with_all:foo,bar,…
- required_without:foo,bar,…
- required_without_all:foo,bar,…
- same:field
- size:value
- string
- timezone
- unique:table,column,except,idColumn
- url
- Conditionally Adding Rules
- Custom Validation Rules
Validation
- Introduction
- Validation Quickstart
- Other Validation Approaches
- Working With Error Messages
- Available Validation Rules
- Conditionally Adding Rules
- Custom Validation Rules
Introduction
Laravel provides several different approaches to validate your application's incoming data. By default, Laravel's base controller class uses a ValidatesRequests
trait which provides a convenient method to validate incoming HTTP request with a variety of powerful validation rules.
Validation Quickstart
To learn about Laravel's powerful validation features, let's look at a complete example of validating a form and displaying the error messages back to the user.
Defining The Routes
First, let's assume we have the following routes defined in our app/Http/routes.php
file:
// Display a form to create a blog post...
Route::get('post/create', '[email protected]');
// Store a new blog post...
Route::post('post', '[email protected]');
Of course, the GET
route will display a form for the user to create a new blog post, while the POST
route will store the new blog post in the database.
Creating The Controller
Next, let's take a look at a simple controller that handles these routes. We'll leave the store
method empty for now:
<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
class PostController extends Controller
{
/**
* Show the form to create a new blog post.
*
* @return Response
*/
public function create()
{
return view('post.create');
}
/**
* Store a new blog post.
*
* @param Request $request
* @return Response
*/
public function store(Request $request)
{
// Validate and store the blog post...
}
}
Writing The Validation Logic
Now we are ready to fill in our store
method with the logic to validate the new blog post. If you examine your application's base controller (App\Http\Controllers\Controller
) class, you will see that the class uses a ValidatesRequests
trait. This trait provides a convenient validate
method in all of your controllers.
The validate
method accepts an incoming HTTP request and a set of validation rules. If the validation rules pass, your code will keep executing normally; however, if validation fails, an exception will be thrown and the proper error response will automatically be sent back to the user. In the case of a traditional HTTP request, a redirect response will be generated, while a JSON response will be sent for AJAX requests.
To get a better understanding of the validate
method, let's jump back into the store
method:
/**
* Store a new blog post.
*
* @param Request $request
* @return Response
*/
public function store(Request $request)
{
$this->validate($request, [
'title' => 'required|unique:posts|max:255',
'body' => 'required',
]);
// The blog post is valid, store in database...
}
As you can see, we simply pass the incoming HTTP request and desired validation rules into the validate
method. Again, if the validation fails, the proper response will automatically be generated. If the validation passes, our controller will continue executing normally.
Stopping On First Validation Failure
Sometimes you may wish to stop running validation rules on an attribute after the first validation failure. To do so, assign the bail
rule to the attribute:
$this->validate($request, [
'title' => 'bail|required|unique:posts|max:255',
'body' => 'required',
]);
In this example, if the required
rule on the title
attribute fails, the unique
rule will not be checked. Rules will be validated in the order they are assigned.
A Note On Nested Attributes
If your HTTP request contains "nested" parameters, you may specify them in your validation rules using "dot" syntax:
$this->validate($request, [
'title' => 'required|unique:posts|max:255',
'author.name' => 'required',
'author.description' => 'required',
]);
Displaying The Validation Errors
So, what if the incoming request parameters do not pass the given validation rules? As mentioned previously, Laravel will automatically redirect the user back to their previous location. In addition, all of the validation errors will automatically be flashed to the session.
Again, notice that we did not have to explicitly bind the error messages to the view in our GET
route. This is because Laravel will check for errors in the session data, and automatically bind them to the view if they are available. The $errors
variable will be an instance of Illuminate\Support\MessageBag
. For more information on working with this object, check out its documentation.
Note: The
$errors
variable is bound to the view by theIlluminate\View\Middleware\ShareErrorsFromSession
middleware, which is provided by theweb
middleware group. When this middleware is applied an$errors
variable will always be available in your views, allowing you to conveniently assume the$errors
variable is always defined and can be safely used.
So, in our example, the user will be redirected to our controller's create
method when validation fails, allowing us to display the error messages in the view:
<!-- /resources/views/post/create.blade.php -->
<h1>Create Post</h1>
@if (count($errors) > 0)
<div class="alert alert-danger">
<ul>
@foreach ($errors->all() as $error)
<li>{{ $error }}</li>
@endforeach
</ul>
</div>
@endif
<!-- Create Post Form -->
Customizing The Flashed Error Format
If you wish to customize the format of the validation errors that are flashed to the session when validation fails, override the formatValidationErrors
on your base controller. Don't forget to import the Illuminate\Contracts\Validation\Validator
class at the top of the file:
<?php
namespace App\Http\Controllers;
use Illuminate\Foundation\Bus\DispatchesJobs;
use Illuminate\Contracts\Validation\Validator;
use Illuminate\Routing\Controller as BaseController;
use Illuminate\Foundation\Validation\ValidatesRequests;
abstract class Controller extends BaseController
{
use DispatchesJobs, ValidatesRequests;
/**
* {@inheritdoc}
*/
protected function formatValidationErrors(Validator $validator)
{
return $validator->errors()->all();
}
}
AJAX Requests & Validation
In this example, we used a traditional form to send data to the application. However, many applications use AJAX requests. When using the validate
method during an AJAX request, Laravel will not generate a redirect response. Instead, Laravel generates a JSON response containing all of the validation errors. This JSON response will be sent with a 422 HTTP status code.
Validating Arrays
Validating array form input fields doesn't have to be a pain. For example, to validate that each e-mail in a given array input field is unique, you may do the following:
$validator = Validator::make($request->all(), [
'person.*.email' => 'email|unique:users',
'person.*.first_name' => 'required_with:person.*.last_name',
]);
Likewise, you may use the *
character when specifying your validation messages in your language files, making it a breeze to use a single validation message for array based fields:
'custom' => [
'person.*.email' => [
'unique' => 'Each person must have a unique e-mail address',
]
],
Other Validation Approaches
Manually Creating Validators
If you do not want to use the ValidatesRequests
trait's validate
method, you may create a validator instance manually using the Validator
facade. The make
method on the facade generates a new validator instance:
<?php
namespace App\Http\Controllers;
use Validator;
use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
class PostController extends Controller
{
/**
* Store a new blog post.
*
* @param Request $request
* @return Response
*/
public function store(Request $request)
{
$validator = Validator::make($request->all(), [
'title' => 'required|unique:posts|max:255',
'body' => 'required',
]);
if ($validator->fails()) {
return redirect('post/create')
->withErrors($validator)
->withInput();
}
// Store the blog post...
}
}
The first argument passed to the make
method is the data under validation. The second argument is the validation rules that should be applied to the data.
After checking if the request failed to pass validation, you may use the withErrors
method to flash the error messages to the session. When using this method, the $errors
variable will automatically be shared with your views after redirection, allowing you to easily display them back to the user. The withErrors
method accepts a validator, a MessageBag
, or a PHP array
.
Named Error Bags
If you have multiple forms on a single page, you may wish to name the MessageBag
of errors, allowing you to retrieve the error messages for a specific form. Simply pass a name as the second argument to withErrors
:
return redirect('register')
->withErrors($validator, 'login');
You may then access the named MessageBag
instance from the $errors
variable:
{{ $errors->login->first('email') }}
After Validation Hook
The validator also allows you to attach callbacks to be run after validation is completed. This allows you to easily perform further validation and even add more error messages to the message collection. To get started, use the after
method on a validator instance:
$validator = Validator::make(...);
$validator->after(function($validator) {
if ($this->somethingElseIsInvalid()) {
$validator->errors()->add('field', 'Something is wrong with this field!');
}
});
if ($validator->fails()) {
//
}
Form Request Validation
For more complex validation scenarios, you may wish to create a "form request". Form requests are custom request classes that contain validation logic. To create a form request class, use the make:request
Artisan CLI command:
php artisan make:request StoreBlogPostRequest
The generated class will be placed in the app/Http/Requests
directory. Let's add a few validation rules to the rules
method:
/**
* Get the validation rules that apply to the request.
*
* @return array
*/
public function rules()
{
return [
'title' => 'required|unique:posts|max:255',
'body' => 'required',
];
}
So, how are the validation rules evaluated? All you need to do is type-hint the request on your controller method. The incoming form request is validated before the controller method is called, meaning you do not need to clutter your controller with any validation logic:
/**
* Store the incoming blog post.
*
* @param StoreBlogPostRequest $request
* @return Response
*/
public function store(StoreBlogPostRequest $request)
{
// The incoming request is valid...
}
If validation fails, a redirect response will be generated to send the user back to their previous location. The errors will also be flashed to the session so they are available for display. If the request was an AJAX request, a HTTP response with a 422 status code will be returned to the user including a JSON representation of the validation errors.
Authorizing Form Requests
The form request class also contains an authorize
method. Within this method, you may check if the authenticated user actually has the authority to update a given resource. For example, if a user is attempting to update a blog post comment, do they actually own that comment? For example:
/**
* Determine if the user is authorized to make this request.
*
* @return bool
*/
public function authorize()
{
$commentId = $this->route('comment');
return Comment::where('id', $commentId)
->where('user_id', Auth::id())->exists();
}
Note the call to the route
method in the example above. This method grants you access to the URI parameters defined on the route being called, such as the {comment}
parameter in the example below:
Route::post('comment/{comment}');
If the authorize
method returns false
, a HTTP response with a 403 status code will automatically be returned and your controller method will not execute.
If you plan to have authorization logic in another part of your application, simply return true
from the authorize
method:
/**
* Determine if the user is authorized to make this request.
*
* @return bool
*/
public function authorize()
{
return true;
}
Customizing The Flashed Error Format
If you wish to customize the format of the validation errors that are flashed to the session when validation fails, override the formatErrors
on your base request (App\Http\Requests\Request
). Don't forget to import the Illuminate\Contracts\Validation\Validator
class at the top of the file:
/**
* {@inheritdoc}
*/
protected function formatErrors(Validator $validator)
{
return $validator->errors()->all();
}
Customizing The Error Messages
You may customize the error messages used by the form request by overriding the messages
method. This method should return an array of attribute / rule pairs and their corresponding error messages:
/**
* Get the error messages for the defined validation rules.
*
* @return array
*/
public function messages()
{
return [
'title.required' => 'A title is required',
'body.required' => 'A message is required',
];
}
Working With Error Messages
After calling the errors
method on a Validator
instance, you will receive an Illuminate\Support\MessageBag
instance, which has a variety of convenient methods for working with error messages.
Retrieving The First Error Message For A Field
To retrieve the first error message for a given field, use the first
method:
$messages = $validator->errors();
echo $messages->first('email');
Retrieving All Error Messages For A Field
If you wish to simply retrieve an array of all of the messages for a given field, use the get
method:
foreach ($messages->get('email') as $message) {
//
}
Retrieving All Error Messages For All Fields
To retrieve an array of all messages for all fields, use the all
method:
foreach ($messages->all() as $message) {
//
}
Determining If Messages Exist For A Field
if ($messages->has('email')) {
//
}
Retrieving An Error Message With A Format
echo $messages->first('email', '<p>:message</p>');
Retrieving All Error Messages With A Format
foreach ($messages->all('<li>:message</li>') as $message) {
//
}
Custom Error Messages
If needed, you may use custom error messages for validation instead of the defaults. There are several ways to specify custom messages. First, you may pass the custom messages as the third argument to the Validator::make
method:
$messages = [
'required' => 'The :attribute field is required.',
];
$validator = Validator::make($input, $rules, $messages);
In this example, the :attribute
place-holder will be replaced by the actual name of the field under validation. You may also utilize other place-holders in validation messages. For example:
$messages = [
'same' => 'The :attribute and :other must match.',
'size' => 'The :attribute must be exactly :size.',
'between' => 'The :attribute must be between :min - :max.',
'in' => 'The :attribute must be one of the following types: :values',
];
Specifying A Custom Message For A Given Attribute
Sometimes you may wish to specify a custom error messages only for a specific field. You may do so using "dot" notation. Specify the attribute's name first, followed by the rule:
$messages = [
'email.required' => 'We need to know your e-mail address!',
];
Specifying Custom Messages In Language Files
In many cases, you may wish to specify your attribute specific custom messages in a language file instead of passing them directly to the Validator
. To do so, add your messages to custom
array in the resources/lang/xx/validation.php
language file.
'custom' => [
'email' => [
'required' => 'We need to know your e-mail address!',
],
],
Available Validation Rules
Below is a list of all available validation rules and their function:
AcceptedActive URLAfter (Date)AlphaAlpha DashAlpha NumericArrayBefore (Date)BetweenBooleanConfirmedDateDate FormatDifferentDigitsDigits BetweenDimensions (Image Files)DistinctE-MailExists (Database)FileFilledImage (File)InIn ArrayIntegerIP AddressJSONMaxMIME TypesMIME Type By File ExtensionMinNot InNumericPresentRegular ExpressionRequiredRequired IfRequired UnlessRequired WithRequired With AllRequired WithoutRequired Without AllSameSizeStringTimezoneUnique (Database)URL
accepted
The field under validation must be yes, on, 1, or true. This is useful for validating "Terms of Service" acceptance.
active_url
The field under validation must be a valid URL according to the checkdnsrr
PHP function.
after:date
The field under validation must be a value after a given date. The dates will be passed into the strtotime
PHP function:
'start_date' => 'required|date|after:tomorrow'
Instead of passing a date string to be evaluated by strtotime
, you may specify another field to compare against the date:
'finish_date' => 'required|date|after:start_date'
alpha
The field under validation must be entirely alphabetic characters.
alpha_dash
The field under validation may have alpha-numeric characters, as well as dashes and underscores.
alpha_num
The field under validation must be entirely alpha-numeric characters.
array
The field under validation must be a PHP array
.
before:date
The field under validation must be a value preceding the given date. The dates will be passed into the PHP strtotime
function.
between:min,max
The field under validation must have a size between the given min and max. Strings, numerics, and files are evaluated in the same fashion as the size
rule.
boolean
The field under validation must be able to be cast as a boolean. Accepted input are true
, false
, 1
, 0
, "1"
, and "0"
.
confirmed
The field under validation must have a matching field of foo_confirmation
. For example, if the field under validation is password
, a matching password_confirmation
field must be present in the input.
date
The field under validation must be a valid date according to the strtotime
PHP function.
date_format:format
The field under validation must match the given format. The format will be evaluated using the PHP date_parse_from_format
function. You should use either date
or date_format
when validating a field, not both.
different:field
The field under validation must have a different value than field.
digits:value
The field under validation must be numeric and must have an exact length of value.
digits_between:min,max
The field under validation must have a length between the given min and max.
dimensions
The file under validation must be an image meeting the dimension constraints as specified by the rule's parameters:
'avatar' => 'dimensions:min_width=100,min_height=200'
Available constraints are: min_width, max_width, min_height, max_height, width, height, ratio.
distinct
When working with arrays, the field under validation must not have any duplicate values.
'foo.*.id' => 'distinct'
The field under validation must be formatted as an e-mail address.
exists:table,column
The field under validation must exist on a given database table.
Basic Usage Of Exists Rule
'state' => 'exists:states'
Specifying A Custom Column Name
'state' => 'exists:states,abbreviation'
You may also specify more conditions that will be added as "where" clauses to the query:
'email' => 'exists:staff,email,account_id,1'
These conditions may be negated using the !
sign:
'email' => 'exists:staff,email,role,!admin'
You may also pass NULL
or NOT_NULL
to the "where" clause:
'email' => 'exists:staff,email,deleted_at,NULL'
'email' => 'exists:staff,email,deleted_at,NOT_NULL'
Occasionally, you may need to specify a specific database connection to be used for the exists
query. You can accomplish this by prepending the connection name to the table name using "dot" syntax:
'email' => 'exists:connection.staff,email'
file
The field under validation must be a successfully uploaded file.
filled
The field under validation must not be empty when it is present.
image
The file under validation must be an image (jpeg, png, bmp, gif, or svg)
in:foo,bar,…
The field under validation must be included in the given list of values.
in_array:anotherfield
The field under validation must exist in anotherfield's values.
integer
The field under validation must be an integer.
ip
The field under validation must be an IP address.
json
The field under validation must be a valid JSON string.
max:value
The field under validation must be less than or equal to a maximum value. Strings, numerics, and files are evaluated in the same fashion as the size
rule.
mimetypes:text/plain,…
The file under validation must match one of the given MIME types:
'video' => 'mimetypes:video/avi,video/mpeg,video/quicktime'
To determine the MIME type of the uploaded file, the file's contents will be read and the framework will attempt to guess the MIME type, which may be different from the client provided MIME type.
mimes:foo,bar,…
The file under validation must have a MIME type corresponding to one of the listed extensions.
Basic Usage Of MIME Rule
'photo' => 'mimes:jpeg,bmp,png'
Even though you only need to specify the extensions, this rule actually validates against the MIME type of the file by reading the file's contents and guessing its MIME type.
A full listing of MIME types and their corresponding extensions may be found at the following location: http://svn.apache.org/repos/asf/httpd/httpd/trunk/docs/conf/mime.types
min:value
The field under validation must have a minimum value. Strings, numerics, and files are evaluated in the same fashion as the size
rule.
not_in:foo,bar,…
The field under validation must not be included in the given list of values.
numeric
The field under validation must be numeric.
present
The field under validation must be present in the input data but can be empty.
regex:pattern
The field under validation must match the given regular expression.
Note: When using the regex
pattern, it may be necessary to specify rules in an array instead of using pipe delimiters, especially if the regular expression contains a pipe character.
required
The field under validation must be present in the input data and not empty. A field is considered "empty" if one of the following conditions are true:
- The value is
null
. - The value is an empty string.
- The value is an empty array or empty
Countable
object. - The value is an uploaded file with no path.
required_if:anotherfield,value,…
The field under validation must be present and not empty if the anotherfield field is equal to any value.
required_unless:anotherfield,value,…
The field under validation must be present and not empty unless the anotherfield field is equal to any value.
required_with:foo,bar,…
The field under validation must be present and not empty only if any of the other specified fields are present.
required_with_all:foo,bar,…
The field under validation must be present and not empty only if all of the other specified fields are present.
required_without:foo,bar,…
The field under validation must be present and not empty only when any of the other specified fields are not present.
required_without_all:foo,bar,…
The field under validation must be present and not empty only when all of the other specified fields are not present.
same:field
The given field must match the field under validation.
size:value
The field under validation must have a size matching the given value. For string data, value corresponds to the number of characters. For numeric data, value corresponds to a given integer value. For an array, size corresponds to the count
of the array. For files, size corresponds to the file size in kilobytes.
string
The field under validation must be a string.
timezone
The field under validation must be a valid timezone identifier according to the timezone_identifiers_list
PHP function.
unique:table,column,except,idColumn
The field under validation must be unique on a given database table. If the column
option is not specified, the field name will be used.
Specifying A Custom Column Name:
'email' => 'unique:users,email_address'
Custom Database Connection
Occasionally, you may need to set a custom connection for database queries made by the Validator. As seen above, setting unique:users
as a validation rule will use the default database connection to query the database. To override this, specify the connection followed by the table name using "dot" syntax:
'email' => 'unique:connection.users,email_address'
Forcing A Unique Rule To Ignore A Given ID:
Sometimes, you may wish to ignore a given ID during the unique check. For example, consider an "update profile" screen that includes the user's name, e-mail address, and location. Of course, you will want to verify that the e-mail address is unique. However, if the user only changes the name field and not the e-mail field, you do not want a validation error to be thrown because the user is already the owner of the e-mail address. You only want to throw a validation error if the user provides an e-mail address that is already used by a different user. To tell the unique rule to ignore the user's ID, you may pass the ID as the third parameter:
'email' => 'unique:users,email_address,'.$user->id
If your table uses a primary key column name other than id
, you may specify it as the fourth parameter:
'email' => 'unique:users,email_address,'.$user->id.',user_id'
Adding Additional Where Clauses:
You may also specify more conditions that will be added as "where" clauses to the query:
'email' => 'unique:users,email_address,NULL,id,account_id,1'
In the rule above, only rows with an account_id
of 1
would be included in the unique check.
url
The field under validation must be a valid URL.
Conditionally Adding Rules
In some situations, you may wish to run validation checks against a field only if that field is present in the input array. To quickly accomplish this, add the sometimes
rule to your rule list:
$v = Validator::make($data, [
'email' => 'sometimes|required|email',
]);
In the example above, the email
field will only be validated if it is present in the $data
array.
Complex Conditional Validation
Sometimes you may wish to add validation rules based on more complex conditional logic. For example, you may wish to require a given field only if another field has a greater value than 100. Or, you may need two fields to have a given value only when another field is present. Adding these validation rules doesn't have to be a pain. First, create a Validator
instance with your static rules that never change:
$v = Validator::make($data, [
'email' => 'required|email',
'games' => 'required|numeric',
]);
Let's assume our web application is for game collectors. If a game collector registers with our application and they own more than 100 games, we want them to explain why they own so many games. For example, perhaps they run a game re-sell shop, or maybe they just enjoy collecting. To conditionally add this requirement, we can use the sometimes
method on the Validator
instance.
$v->sometimes('reason', 'required|max:500', function($input) {
return $input->games >= 100;
});
The first argument passed to the sometimes
method is the name of the field we are conditionally validating. The second argument is the rules we want to add. If the Closure
passed as the third argument returns true
, the rules will be added. This method makes it a breeze to build complex conditional validations. You may even add conditional validations for several fields at once:
$v->sometimes(['reason', 'cost'], 'required', function($input) {
return $input->games >= 100;
});
Note: The
$input
parameter passed to yourClosure
will be an instance ofIlluminate\Support\Fluent
and may be used to access your input and files.
Custom Validation Rules
Laravel provides a variety of helpful validation rules; however, you may wish to specify some of your own. One method of registering custom validation rules is using the extend
method on the Validator
facade. Let's use this method within a service provider to register a custom validation rule:
<?php
namespace App\Providers;
use Validator;
use Illuminate\Support\ServiceProvider;
class AppServiceProvider extends ServiceProvider
{
/**
* Bootstrap any application services.
*
* @return void
*/
public function boot()
{
Validator::extend('foo', function($attribute, $value, $parameters, $validator) {
return $value == 'foo';
});
}
/**
* Register the service provider.
*
* @return void
*/
public function register()
{
//
}
}
The custom validator Closure receives four arguments: the name of the $attribute
being validated, the $value
of the attribute, an array of $parameters
passed to the rule, and the Validator
instance.
You may also pass a class and method to the extend
method instead of a Closure:
Validator::extend('foo', '[email protected]');
Defining The Error Message
You will also need to define an error message for your custom rule. You can do so either using an inline custom message array or by adding an entry in the validation language file. This message should be placed in the first level of the array, not within the custom
array, which is only for attribute-specific error messages:
"foo" => "Your input was invalid!",
"accepted" => "The :attribute must be accepted.",
// The rest of the validation error messages...
When creating a custom validation rule, you may sometimes need to define custom place-holder replacements for error messages. You may do so by creating a custom Validator as described above then making a call to the replacer
method on the Validator
facade. You may do this within the boot
method of a service provider:
/**
* Bootstrap any application services.
*
* @return void
*/
public function boot()
{
Validator::extend(...);
Validator::replacer('foo', function($message, $attribute, $rule, $parameters) {
return str_replace(...);
});
}
Implicit Extensions
By default, when an attribute being validated is not present or contains an empty value as defined by the required
rule, normal validation rules, including custom extensions, are not run. For example, the unique
rule will not be run against a null
value:
$rules = ['name' => 'unique'];
$input = ['name' => null];
Validator::make($input, $rules)->passes(); // true
For a rule to run even when an attribute is empty, the rule must imply that the attribute is required. To create such an "implicit" extension, use the Validator::extendImplicit()
method:
Validator::extendImplicit('foo', function($attribute, $value, $parameters, $validator) {
return $value == 'foo';
});
Note: An "implicit" extension only implies that the attribute is required. Whether it actually invalidates a missing or empty attribute is up to you.