erDiagram
    Avatar }o--|| Photo : "uses photo"
    Photo ||--o{ BreweryPhoto : "used in"
    Photo ||--o{ BeerPhoto : "used in"

    %% Cross-schema: defined in full in identity.mmd / brewery.mmd / beer.mmd
    Profile ||--o{ Avatar : "has avatar history"
    User ||--o{ Photo : "uploads"
    Brewery ||--o{ BreweryPhoto : "has photos"
    Beer ||--o{ BeerPhoto : "has photos"

    Photo {
        uniqueidentifier PhotoID PK
        nvarchar Hyperlink "nullable"
        uniqueidentifier UploadedByID FK
        datetime UploadedAt
    }

    Avatar {
        uniqueidentifier UserAvatarID PK
        uniqueidentifier UserProfileID FK
        uniqueidentifier PhotoID FK
        datetime2 ValidFrom
        datetime2 ValidTo "nullable; at most one row per UserProfileID has ValidTo IS NULL (active avatar)"
    }

    BreweryPhoto {
        uniqueidentifier BreweryPostPhotoID PK
        uniqueidentifier BreweryPostID FK
        uniqueidentifier PhotoID FK
        datetime LinkedAt
    }

    BeerPhoto {
        uniqueidentifier BeerPostPhotoID PK
        uniqueidentifier BeerPostID FK
        uniqueidentifier PhotoID FK
        datetime LinkedAt
    }