Updated db diagram again.

Signed-off-by: Cliff Hill <xlorep@darkhelm.org>

README.md

@@ -211,37 +211,34 @@ Enter the password when prompted (see your `.env` file, default is `password`).
 #### Database Schema Diagram
 
 ```mermaid
-erDiagram
-  USERS {
-    string email PK
+classDiagram
+  class User {
+    string email
     string name
   }
-  ROOMS {
-    int id PK
-    string name UNIQUE
+  class Room {
+    int id
+    string name
     string location
     string equipment
     int capacity
   }
-  BOOKINGS {
-    int id PK
-    int room_id FK
+  class Booking {
+    int id
+    int room_id
     datetime start_time
     datetime end_time
     string title
   }
-  INVITEES {
-    int id PK
-    int booking_id FK
-    string user_email FK
+  class Invitee {
+    int id
+    int booking_id
+    string user_email
   }
 
-  USERS ||--o{ INVITEES : has
-  ROOMS ||--o{ BOOKINGS : contains
-  BOOKINGS ||--o{ INVITEES : includes
-  BOOKINGS }o--|| ROOMS : "booked in"
-  INVITEES }o--|| USERS : "is user"
-  INVITEES }o--|| BOOKINGS : "for booking"
+  User "1" <|-- "*" Invitee : user_email
+  Room "1" <|-- "*" Booking : room_id
+  Booking "1" <|-- "*" Invitee : booking_id
 ```
 
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