silverstripe-framework/docs/en/topics/form-validation.md

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# Form Validation
SilverStripe provides PHP form validation out of the box,
but doesn't come with any built-in JavaScript validation
(the previously used `Validator.js` approach has been deprecated).
## Required Fields
Validators are implemented as an argument to the `[api:Form]` constructor,
and are subclasses of the abstract `[api:Validator]` base class.
The only implementation which comes with SilverStripe is
the `[api:RequiredFields]` class, which ensures fields are filled out
when the form is submitted.
:::php
public function Form() {
$form = new Form($this, 'Form',
new FieldList(
new TextField('MyRequiredField'),
new TextField('MyOptionalField')
),
new FieldList(
new FormAction('submit', 'Submit form')
),
new RequiredFields(array('MyRequiredField'))
);
// Optional: Add a CSS class for custom styling
$form->dataFieldByName('MyRequiredField)->addExtraClass('required');
return $form;
}
## Form Field Validation
Form fields are responsible for validating the data they process,
through the `[api:FormField->validate()] method. There are many fields
for different purposes (see ["form field types"](/reference/form-field-types) for a full list).
## Adding your own validation messages
In many cases, you want to add PHP validation which is more complex than
validating the format or existence of a single form field input.
For example, you might want to have dependent validation on
a postcode which depends on the country you've selected in a different field.
There's two ways to go about this: Either you can attach a custom error message
to a specific field, or a generic message for the whole form.
Example: Validate postcodes based on the selected country (on the controller).
:::php
class MyController extends Controller {
public function Form() {
return Form::create($this, 'Form',
new FieldList(
new NumericField('Postcode'),
new CountryDropdownField('Country')
),
new FieldList(
new FormAction('submit', 'Submit form')
),
new RequiredFields(array('Country'))
);
}
public function submit($data, $form) {
// At this point, RequiredFields->validate() will have been called already,
// so we can assume that the values exist.
// German postcodes need to be five digits
if($data['Country'] == 'de' && isset($data['Postcode']) && strlen($data['Postcode']) != 5) {
$form->addErrorMessage('Postcode', 'Need five digits for German postcodes', 'bad');
return $this->redirectBack();
}
// Global validation error (not specific to form field)
if($data['Country'] == 'IR' && isset($data['Postcode']) && $data['Postcode']) {
$form->sessionMessage("Ireland doesn't have postcodes!", 'bad');
return $this->redirectBack();
}
// continue normal processing...
}
}
## JavaScript Validation
While 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.
### HTML5 attributes
HTML5 specifies some built-in form validations ([source](http://www.w3.org/wiki/HTML5_form_additions)),
which are evaluated by modern browsers without any need for JavaScript.
SilverStripe supports this by allowing to set custom attributes on fields.
:::php
// Markup contains <input type="text" required />
TextField::create('MyText')->setAttribute('required', true);
// Markup contains <input type="url" pattern="https?://.+" />
TextField::create('MyText')
->setAttribute('type', 'url')
->setAttribute('pattern', 'https?://.+')
### HTML5 metadata
In addition, HTML5 elements can contain custom data attributes with the `data-` prefix.
These are general purpose attributes, but can be used to hook in your own validation.
:::php
// Validate a specific date format (in PHP)
// Markup contains <input type="text" data-dateformat="dd.MM.yyyy" />
DateField::create('MyDate')->setConfig('dateformat', 'dd.MM.yyyy');
// Limit extensions on upload (in PHP)
// Markup contains <input type="file" data-allowed-extensions="jpg,jpeg,gif" />
$exts = array('jpg', 'jpeg', 'gif');
$validator = new Upload_Validator();
$validator->setAllowedExtensions($exts);
$upload = Upload::create()->setValidator($validator);
$fileField = FileField::create('MyFile')->setUpload(new);
$fileField->setAttribute('data-allowed-extensions', implode(',', $exts));
Note that these examples don't have any effect on the client as such,
but are just a starting point for custom validation with JavaScript.
## Model Validation
An alternative (or additional) approach to validation is to place it directly
on the model. SilverStripe provides a `[api:DataObject->validate()]` method for this purpose.
Refer to the ["datamodel" topic](/topics/datamodel#validation-and-constraints) for more information.
## Subclassing Validator
To create your own validator, you need to subclass validator and define two methods:
* **javascript()** Should output a snippet of JavaScript that will get called to perform javascript validation.
* **php($data)** Should return true if the given data is valid, and call $this->validationError() if there were any
errors.
## Related
* Model Validation with [api:DataObject->validate()]