OpenAPI: Support for JSON-LD Only APIs

[soyuka]

Context

When building a JSON-LD only API (no plain JSON format), the OpenAPI specification still generates duplicate schemas and content types. Users have to create custom OpenApiFactory decorators to filter these out.

Current Behavior

With this configuration:

api_platform:
    formats:
        jsonld: ['application/ld+json']
    error_formats:
        jsonld: ['application/ld+json']
        jsonproblem: ['application/problem+json']

The OpenAPI export still produces:

1. Duplicate schemas: EmailMessage AND EmailMessage.jsonld
2. Multiple content types in responses: application/ld+json, application/problem+json, application/json

Workaround We Implemented

We created an OpenApiFactory decorator that:

1. Filters non-JSON-LD content types from responses

private const NON_JSONLD_MIME_TYPES = [
    'text/html',
    'application/problem+json',
    'application/json',
];

private function filterNonJsonContentTypes(PathItem $pathItem): PathItem
{
    foreach (PathItem::$methods as $method) {
        $operation = $pathItem->{"get" . ucfirst(strtolower($method))}();
        if (null === $operation) continue;

        foreach ($operation->getResponses() as $status => $response) {
            $content = $response->getContent();
            if ($content) {
                $filteredContent = new \ArrayObject();
                foreach ($content as $mimeType => $mediaType) {
                    if (!in_array($mimeType, self::NON_JSONLD_MIME_TYPES, true)) {
                        $filteredContent[$mimeType] = $mediaType;
                    }
                }
                // ... update response
            }
        }
    }
    return $pathItem;
}

2. Removes duplicate schemas (keeps only .jsonld versions)

private function filterNonJsonSchemas(OpenApi $openApi): OpenApi
{
    $schemas = $openApi->getComponents()->getSchemas();

    // Collect base names that have .jsonld versions
    $jsonldSchemas = [];
    foreach ($schemas as $name => $schema) {
        if (str_ends_with($name, '.jsonld')) {
            $jsonldSchemas[substr($name, 0, -7)] = true;
        }
    }

    $filteredSchemas = new \ArrayObject();
    foreach ($schemas as $name => $schema) {
        $baseName = preg_replace('/\.jsonld$/', '', $name);

        // Skip non-.jsonld version when .jsonld exists
        if (!str_ends_with($name, '.jsonld') && isset($jsonldSchemas[$baseName])) {
            continue;
        }

        $filteredSchemas[$name] = $schema;
    }

    return $openApi->withComponents($components->withSchemas($filteredSchemas));
}

Proposed Framework Enhancement

Option A: openapi.prefer_format Configuration

Add a configuration option to specify the preferred format for OpenAPI documentation:

api_platform:
    openapi:
        prefer_format: jsonld  # Only show jsonld schemas and content types

Implementation:

In OpenApiFactory, when prefer_format is set:

1. Only generate schemas for that format (skip others even if configured)
2. Only include that format's content type in responses
3. Remove duplicate schemas that exist in multiple format variants

Option B: openapi.formats Configuration

Allow explicit control over which formats appear in OpenAPI (separate from runtime formats):

api_platform:
    formats:
        jsonld: ['application/ld+json']
        json: ['application/json']  # Available at runtime
    openapi:
        formats:
            jsonld: ['application/ld+json']  # Only this in docs

Implementation:

In OpenApiFactory::getMimeTypes():

private function getMimeTypes(HttpOperation $operation): array
{
    // Use openapi.formats if configured, otherwise fall back to operation formats
    $responseFormats = $this->openapiFormats
        ?? $operation->getOutputFormats()
        ?? [];

    // ... rest of method
}

Option C: Automatic Deduplication

When multiple formats produce equivalent schemas (same structure, different naming), automatically deduplicate:

// In OpenApiFactory::collectPaths() or a new dedicated method
private function deduplicateSchemas(\ArrayObject $schemas): \ArrayObject
{
    $dominated = [];

    // jsonld dominates json (more specific)
    foreach ($schemas as $name => $schema) {
        if (str_ends_with($name, '.jsonld')) {
            $baseName = substr($name, 0, -7);
            if (isset($schemas[$baseName])) {
                $dominated[$baseName] = true;
            }
        }
    }

    // Remove dominated schemas
    foreach ($dominated as $name => $_) {
        unset($schemas[$name]);
    }

    return $schemas;
}

Recommendation

Option A (prefer_format) is the cleanest because:

1. Simple, single configuration option
2. Clear intent: "I want my OpenAPI docs in this format"
3. Doesn't affect runtime behavior
4. Easy to understand and document

Example implementation location:

• Configuration: src/Symfony/Bundle/DependencyInjection/Configuration.php
• Logic: src/OpenApi/Factory/OpenApiFactory.php

Additional Consideration: Accept/Content-Type Headers

Our decorator also adds Accept and Content-Type header parameters to all operations, showing available formats as an enum. This is useful documentation that API Platform could generate automatically.

parameters:
  - name: Accept
    in: header
    schema:
      type: string
      enum: ['application/ld+json']
      default: 'application/ld+json'

This could be another configuration option:

api_platform:
    openapi:
        document_content_negotiation_headers: true