Add Users and Memberships to the ERD

docs/data-model.md

@@ -62,6 +62,19 @@ erDiagram
     string trn FK "Primary key for people in DQT"
   }
 
+  User {
+    uuid id PK
+    string email UK
+  }
+
+  Membership {
+    uuid id PK
+    uuid user_id FK
+    string organisation_type FK "Polymorphic association with School or Provider"
+    string organisation_id FK "Polymorphic association with School or Provider"
+    enum service "Placements or Claims"
+  }
+
   GiasSchool {
     uuid id PK
     string urn UK "Unique identifier for Schools"
@@ -83,6 +96,10 @@ erDiagram
 
   School ||--|{ Claim : "has many"
   Claim }|--|{ MentorTraining : "has and belongs to many"
+
+  User ||--|{ Membership : "has many"
+  Membership }|--o| Provider : "belongs to (polymorphic)"
+  Membership }|--o| School : "belongs to (polymorphic)"
 ```
 
 ## Onboarding Schools and Providers into the services
@@ -120,3 +137,18 @@ Onboarded Providers will have a record in the `providers` table.
 Providers are only onboarded into the School Placements service, because this is the only service Provider Users will need to sign in to. Providers will not sign in to the Track & Pay service.
 
 Both services will query the Provider endpoints on the [Teacher Training Courses API](https://api.publish-teacher-training-courses.service.gov.uk/docs/api-reference.html) to retrieve and display information about a Provider given its Accredited Provider ID.
+
+## Users and Organisations
+
+Users are members of Organisations.
+
+Organisation is a polymorphic association which represents either a School or a Provider.
+
+Users can have many Memberships with Organisations (Schools or Providers). Membership acts as the join table between Users and Schools/Providers.
+
+Memberships are also scoped by `service`, which will be either `"placements"` or `"claims"`. This means that, for example, a User belonging to a School in the Track & Pay service won't be able to login to the School Placements service and manage Placements for that same School. They'll need to be added to the User list of each service independently if they need to login to both.
+
+We can therefore define the following composite indexes:
+
+- `[service, user_id]`
+- `[organisation_type, organisation_id]`