Introduction

You may need to validate JSON with constraints beyond what is defined in Draft4 of the JSON Schema specification. To add validaton rules you can either define a custom rule set or write a format extension.

Rule Sets

Internally JSON Guard uses rule sets, which are composed of constraints. The rule set is just a PSR-11 container of constraints identified by the validation keyword. By default the Draft4 rule set is used, which corresponds to Draft 4 of the JSON Schema specification. You can easily provide your own rule set by passing it as a constructor parameter.

<?php

$data    = json_decode('{ "id": "json-guard.dev/schema#" }');
$schema  = json_decode('{ "properties": { "id": { "type": "string", "format": "uri" } } }');
$ruleset = new CustomRuleset();

$validator = new Validator($data, $schema, $ruleset);

Format Extensions

JSON Schema allows defining formats like ipv4 that strings will be validated against. You can extend the validator with your own formats.

Usage

The following example shows a simple extension to validate twitter handles. The extension must take a value and pointer, and return a ValidationError if the value is invalid.

<?php

use League\JsonGuard\Constraint\DraftFour\Format\FormatExtensionInterface;
use League\JsonGuard\Validator;

class TwitterHandleFormatExtension implements FormatExtensionInterface
{
    public function validate($value, Validator $validator)
    {
        if (stripos($value, '@') !== 0) {
            return \League\JsonGuard\error('A twitter handle must start with "@"', $validator);
        }
    }
}

Once the extension is written, you can register it with the format constraint.

<?php

$schema = json_decode('{"format": "twitter-handle"}');
$data = '@PHP_CEO';

$validator = new Validator($data, $schema);
$validator->getRuleset()->get('format')->addExtension('twitter-handle', new TwitterHandleFormatExtension());