JSON Schema Support

JSON Schema is a popular vocabulary to describe the shape of JSON documents. A variant of JSON Schema is also used in OpenAPI specifications.

API Platform provides an infrastructure to generate JSON Schemas for any resource, represented in any format (including JSON-LD). The generated schema can be used with libraries such as react-json-schema-form to build forms for the documented resources, or to be used for validation.

Generating a JSON Schema

To export the schema corresponding to an API Resource, run the following command:

docker compose exec php \
    bin/console api:json-schema:generate 'App\Entity\Book'

To see all options available, try:

docker compose exec php \
    bin/console help api:json-schema:generate

Overriding the JSON Schema Specification

In a unit testing context, API Platform does not use the same schema version as the schema used when generating the API documentation. The version used by the documentation is the OpenAPI Schema version and the version used by unit testing is the JSON Schema version.

When Testing the API, JSON Schemas are useful to generate and automate unit testing. API Platform provides specific unit testing functionalities like assertMatchesResourceCollectionJsonSchema() or assertMatchesResourceItemJsonSchema() methods. These methods generate a JSON Schema then do unit testing based on the generated schema automatically.

Usually, the fact that API Platform uses a different schema version for unit testing is not a problem, but sometimes you may need to use the ApiProperty attribute to specify a calculated field type by overriding the OpenAPI Schema for the calculated field to be correctly documented.

When you will use assertMatchesResourceCollectionJsonSchema() or assertMatchesResourceItemJsonSchema() functions the unit test will fail on this calculated field as the unit testing process doesn't use the openapi_context you specified because API Platform is using the JSON Schema version instead at this moment.

So there is a way to override JSON Schema specification for a specific property in the JSON Schema used by the unit testing process.

You will need to add the json_schema_context property in the ApiProperty attribute to do this, example:

<?php

namespace App\Entity;

use ApiPlatform\Metadata\ApiResource;
use Doctrine\ORM\Mapping as ORM;

#[ORM\Entity]
#[ApiResource]
class Greeting
{
    #[ORM\Id, ORM\Column, ORM\GeneratedValue]
    private ?int $id = null;
    
    // [...]

    public function getId(): ?int
    {
        return $this->id;
    }

    #[ApiProperty(
        openapiContext: [
            'type' => 'array',
            'items' => ['type' => 'integer']
        ],
        jsonSchemaContext: [
            'type' => 'array',
            'items' => ['type' => 'integer']
        ]
    )]
    public function getSomeNumbers(): array {
        return [1, 2, 3, 4];
    }
}

You can obtain more information about the available JSON Schema Types and format here.

Generating a JSON Schema Programmatically

To generate JSON Schemas programmatically, use the api_platform.json_schema.schema_factory service.

Testing

API Platform provides a PHPUnit assertion to test if a response is valid according to a given Schema: assertMatchesJsonSchema(). Refer to the testing documentation for more details.