silverstripe-framework/docs/en/02_Developer_Guides/03_Forms/01_Validation.md

title: Form Validation summary: Validate form data through the server side validation API.

Form Validation

SilverStripe provides server-side form validation out of the box through the [api:Validator] class and its' child class [api:RequiredFields]. A single Validator instance is set on each Form. Validators are implemented as an argument to the [api:Form] constructor or through the function setValidator.

:::php
<?php

class Page_Controller extends ContentController {

	private static $allowed_actions = array(
		'MyForm'
	);

	public function MyForm() {
		$fields = new FieldList(
			TextField::create('Name'),
			EmailField::create('Email')
		);

		$actions = new FieldList(
			FormAction::create('doSubmitForm', 'Submit')
		);

		// the fields 'Name' and 'Email' are required.
		$required = new RequiredFields(array(
			'Name', 'Email'
		));

		// $required can be set as an argument
		$form = new Form($controller, 'MyForm', $fields, $actions, $required);

		// Or, through a setter.
		$form->setValidator($required);

		return $form;
	}

	public function doSubmitForm($data, $form) {
		//..
	}
}

In this example we will be required to input a value for Name and a valid email address for Email before the doSubmitForm method is called.

Each individual [api:FormField] instance is responsible for validating the submitted content through the [api:FormField::validate()] method. By default, this just checks the value exists. Fields like `EmailField` override `validate` to check for a specific format.

Subclasses of FormField can define their own version of validate to provide custom validation rules such as the above example with the Email validation. The validate method on FormField takes a single argument of the current Validator instance.

The data value of the `FormField` submitted is not passed into validate. It is stored in the `value` property through the `setValue` method.

:::php
public function validate($validator) {
	if($this->Value() == 10) {
	    $validator->validationError($this->Name(), 'This value cannot be 10');
		return false;
	}

	return true;
}

The validate method should return true if the value passes any validation and false if SilverStripe should trigger a validation error on the page. In addition a useful error message must be set on the given validator.

You can also override the entire `Form` validation by subclassing `Form` and defining a `validate` method on the form.

Say we need a custom FormField which requires the user input a value in a TextField between 2 and 5. There would be two ways to go about this:

A custom FormField which handles the validation. This means the FormField can be reused throughout the site and have the same validation logic applied to it throughout.

mysite/code/formfields/CustomNumberField.php

:::php
<?php

class CustomNumberField extends TextField {

	public function validate($validator) {
		if(!is_numeric($this->value)) {
			$validator->validationError(
				$this->name, "Not a number. This must be between 2 and 5", "validation", false
			);
			
			return false;
		}
		else if($this->value > 5 || $this->value < 2) {
			$validator->validationError(
				$this->name, "Your number must be between 2 and 5", "validation", false
			);

			return false;
		}

		return true;
	}
}

Or, an alternative approach to the custom class is to define the behavior inside the Form's action method. This is less reusable and would not be possible within the CMS or other automated UI but does not rely on creating custom FormField classes.

:::php
<?php

class Page_Controller extends ContentController {

	private static $allowed_actions = array(
		'MyForm'
	);

	public function MyForm() {
		$fields = new FieldList(
			TextField::create('Name'),
			EmailField::create('Email')
		);

		$actions = new FieldList(
			FormAction::create('doSubmitForm', 'Submit')
		);

		$form = new Form($controller, 'MyForm', $fields, $actions);

		return $form;
	}

	public function doSubmitForm($data, $form) {
		// At this point, RequiredFields->isValid() will have been called already,
		// so we can assume that the values exist. Say we want to make sure that email hasn't already been used.
		
		$check = Member::get()->filter('Email', $data['Email'])->first();

		if($check) {
			$form->addErrorMessage('Email', 'This email already exists', 'bad');

			return $this->redirectBack();
		}


		$form->sessionMessage("You have been added to our mailing list", 'good');
		
		return $this->redirectBack();
	}
}

Exempt validation actions

In some cases you might need to disable validation for specific actions. E.g. actions which discard submitted data may not need to check the validity of the posted content.

You can disable validation on individual using one of two methods:

:::php
$actions = new FieldList(
	$action = FormAction::create('doSubmitForm', 'Submit')
);
$form = new Form($controller, 'MyForm', $fields, $actions);

// Disable actions on the form action themselves
$action->setValidationExempt(true);

// Alternatively, you can whitelist individual actions on the form object by name
$form->setValidationExemptActions(['doSubmitForm']);

Server-side validation messages

If a FormField fails to pass validate() the default error message is returned.

:::php
'$Name' is required

Use setCustomValidationMessage to provide a custom message.

:::php
$field = new TextField(..);
$field->setCustomValidationMessage('Whoops, looks like you have missed me!');

JavaScript validation

Although there are no built-in JavaScript validation handlers in SilverStripe, the FormField API is flexible enough to provide the information required in order to plug in custom libraries like Parsley.js or jQuery.Validate. Most of these libraries work on HTML data- attributes or special classes added to each input. For Parsley we can structure the form like.

:::php
$form = new Form(..);
$form->setAttribute('data-parsley-validate', true);

$field = $fields->dataFieldByName('Name');

$field->setAttribute('required', true);
$field->setAttribute('data-parsley-mincheck', '2');

Model Validation

An alternative (or additional) approach to validation is to place it directly on the database model. SilverStripe provides a [api:DataObject::validate()] method to validate data at the model level. See Data Model Validation.

Form action validation

At times it's not possible for all validation or recoverable errors to be pre-determined in advance of form submission, such as those generated by the form [api:Validator] object. Sometimes errors may occur within form action methods, and it is necessary to display errors on the form after initial validation has been performed.

In this case you may throw a [api:ValidationException] object within your handler, optionally passing it an error message, or a [api:ValidationResult] object containing the list of errors you wish to display.

E.g.

:::php
class MyController extends Controller
{
    public function doSave($data, $form) {
        $success = $this->sendEmail($data);
        
        // Example error handling
        if (!$success) {
            throw new ValidationException('Sorry, we could not email to that address');
        }
        
        // If success
        return $this->redirect($this->Link('success'));
    }
}

Validation in the CMS

In the CMS, we're not creating the forms for editing CMS records. The Form instance is generated for us so we cannot call setValidator easily. However, a DataObject can provide its' own Validator instance through the getCMSValidator() method. The CMS interfaces such as [api:LeftAndMain], [api:ModelAdmin] and [api:GridField] will respect the provided Validator and handle displaying error and success responses to the user.

Again, custom error messages can be provided through the `FormField`

:::php
<?php

class Page extends SiteTree {

	private static $db = array(
		'MyRequiredField' => 'Text'
	);

	public function getCMSFields() {
		$fields = parent::getCMSFields();

		$fields->addFieldToTab('Root.Main', 
			TextField::create('MyRequiredField')->setCustomValidationMessage('You missed me.')
		);
	}
	
	public function getCMSValidator() {
		return new RequiredFields(array(
			'MyRequiredField'
		));
	}

API Documentation

• [api:RequiredFields]
• [api:Validator]