fete/specs/012-link-preview/data-model.md

Data Model: Link Preview (Open Graph Meta-Tags)

Feature: 012-link-preview | Date: 2026-03-09

Overview

This feature does NOT introduce new database entities. It reads existing event data and projects it into HTML meta-tags. The "model" here is the meta-tag value object used during HTML generation.

Meta-Tag Value Objects

OpenGraphMeta

Represents the set of Open Graph meta-tags to inject into the HTML response.

Field	Type	Source	Rules
title	String	Event title or "fete"	Max 70 chars, truncated with "..."
description	String	Composed from event fields or generic text	Max 200 chars
url	String	Canonical URL from request	Absolute URL
type	String	Always "website"	Constant
siteName	String	Always "fete"	Constant
image	String	Static brand image URL	Absolute URL to /og-image.png

TwitterCardMeta

Field	Type	Source	Rules
card	String	Always "summary"	Constant
title	String	Same as OG title	Max 70 chars
description	String	Same as OG description	Max 200 chars

Data Flow

Request for /events/{token}
    │
    ▼
LinkPreviewController
    │
    ├── Resolve event token → Event domain object (existing EventRepository)
    │
    ├── Build OpenGraphMeta from Event fields:
    │     title     ← event.title (truncated)
    │     description ← formatDescription(event.dateTime, event.timezone, event.location, event.description)
    │     url       ← request base URL + /events/{token}
    │     image     ← request base URL + /og-image.png
    │
    ├── Build TwitterCardMeta (mirrors OG values)
    │
    ├── Inject meta-tags into cached index.html template
    │
    └── Return modified HTML

Request for / or /create (non-event pages)
    │
    ▼
LinkPreviewController
    │
    ├── Build generic OpenGraphMeta:
    │     title       ← "fete"
    │     description ← "Privacy-focused event planning. Create and share events without accounts."
    │     url         ← request URL
    │     image       ← request base URL + /og-image.png
    │
    ├── Build generic TwitterCardMeta
    │
    ├── Inject meta-tags into cached index.html template
    │
    └── Return modified HTML

Existing Entities Used (Read-Only)

Event (from de.fete.domain.model.Event)

Field	Used For
title	og:title, twitter:title
description	Part of og:description, twitter:description
dateTime	Part of og:description (formatted)
timezone	Date formatting context
location	Part of og:description
eventToken	URL construction