A hierarchy of objects to be serialized into JSON in a single array

Objects.cs

public class StreamItemDTO
{
    public required long Id { get; set; }
    public required string Type { get; set; }
    public long? MediaId { get; set; }

    public required string Title { get; set; }
    public required string Description { get; set; }

    public required DateTime Timestamp { get; set; }
}

public class EventStreamItemDTO : StreamItemDTO
{
    public required long EventTypeId { get; set; }
    public required string EventType { get; set; }
    public required DateTime EventDate { get; set; }
    public string MediaUrl { get; set; } = string.Empty;
    public string MediaPreviewUrl { get; set; } = string.Empty;
    public string MediaThumbnailUrl { get; set; } = string.Empty;
}

public class NewsStreamItemDTO : StreamItemDTO
{
    public string MediaUrl { get; set; } = string.Empty;
    public string MediaPreviewUrl { get; set; } = string.Empty;
    public string MediaThumbnailUrl { get; set; } = string.Empty;
}

public class PhotoStreamItemDTO : StreamItemDTO
{
    public required int Likes { get; set; }
    public required int Comments { get; set; }
    public required string MediaUrl { get; set; }
    public required string MediaPreviewUrl { get; set; }
    public required string MediaThumbnailUrl { get; set; }
}