Every PhotoRecord belongs to exactly one Project through its projectId, which is what lets Relic group all photographs of a single dig together and number them sequentially. Because the photoNumber is only guaranteed unique within a project, the projectId is the other half of that pairing — two different projects can each have a photo number 001 without colliding. The field is required, so a photograph can never be filed without a parent project, and it is indexed for fast project-scoped photo browsing.
Technical section
Data model, API, and internals — visible to developers.