Description

When previewing a page that contains a snippet_selection property, the preview fails with a ContentNotFoundException. This happens because ContentResolver re-aggregates snippets using the parent's stage (draft in preview mode), but snippets only have live dimension content available.

Sulu Version

• Sulu 3.0.1
• Symfony 7.2

Steps to Reproduce

1. Create a snippet template (e.g., beer.xml)
2. Create a page template with a snippet_selection property:

<property name="beers" type="snippet_selection">
    <params>
        <param name="types" value="beer"/>
    </params>
</property>

3. Create and publish a snippet
4. Create a page, select the published snippet in the snippet_selection field
5. Observe the preview panel - it shows an error

Expected Behavior

The preview should display the page with the resolved snippet content.

Actual Behavior

Preview fails with:

ContentNotFoundException: Could not load content with id "019b6573-9aa4-7188-899a-f0d2c31084f7" and attributes: {"locale":"en","stage":"draft"}

Root Cause Analysis

The issue is in ContentResolver.php at lines 75-80:

if ($resource instanceof ContentRichEntityInterface) {
    $childContent = $this->contentAggregator->aggregate($resource, [
        'locale' => $locale,
        'stage' => $stage,  // BUG: Uses parent's stage (draft in preview)
    ]);

Flow:

1. SnippetResourceLoader correctly loads snippets with STAGE_LIVE
2. It returns Snippet entities (which implement ContentRichEntityInterface)
3. ContentResolver sees these are ContentRichEntityInterface instances
4. It re-aggregates them using the parent's stage (draft in preview mode)
5. ContentAggregator can't find dimension content with stage=draft for the snippet
6. ContentNotFoundException is thrown

Why snippets don't have draft content:
Snippets are typically only published (live), not kept in draft state like pages being edited. When a user selects a snippet in a page, they expect to see the published version.

Suggested Fix

Snippets should always be resolved with STAGE_LIVE, regardless of the parent's stage. Possible solutions:

Option 1: Check resource type in ContentResolver

if ($resource instanceof ContentRichEntityInterface) {
    $childStage = $resource instanceof SnippetInterface 
        ? DimensionContentInterface::STAGE_LIVE 
        : $stage;
    
    $childContent = $this->contentAggregator->aggregate($resource, [
        'locale' => $locale,
        'stage' => $childStage,
    ]);

Option 2: Have SnippetResourceLoader return resolved DimensionContent

Instead of returning the Snippet entity, return the already-aggregated DimensionContent with STAGE_LIVE. This bypasses the ContentRichEntityInterface check.

Workaround

We implemented a custom SnippetResourceLoader that fully resolves snippets with STAGE_LIVE and returns the resolved data structure, bypassing the re-aggregation:

class PreviewSafeSnippetResourceLoader implements ResourceLoaderInterface
{
    public function load(array $ids, ?string $locale, array $params = []): array
    {
        // Load snippets with STAGE_LIVE
        $snippets = $this->snippetRepository->findBy([
            'uuids' => $ids,
            'locale' => $locale,
            'stage' => DimensionContentInterface::STAGE_LIVE,
        ], [], [SnippetRepositoryInterface::GROUP_SELECT_SNIPPET_WEBSITE => true]);

        $contentResolver = $this->container->get('sulu_content.content_resolver');

        $mappedResult = [];
        foreach ($snippets as $snippet) {
            $dimensionContent = $this->contentAggregator->aggregate($snippet, [
                'locale' => $locale,
                'stage' => DimensionContentInterface::STAGE_LIVE,
            ]);
            
            // Return fully resolved data instead of entity
            $mappedResult[$snippet->getId()] = $contentResolver->resolve($dimensionContent);
        }

        return $mappedResult;
    }
}

Related

This may be related to similar issues with referenced content in preview mode.