Opened 110 minutes ago

#35941 new New feature

Add composite GenericForeignKey support

Reported by: Csirmaz Bendegúz Owned by:
Component: Database layer (models, ORM) Version: dev
Severity: Normal Keywords:
Cc: Csirmaz Bendegúz Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

This is a follow up to #373 (CompositePrimaryKey).

Proposal:

My proposal is to implement GenericForeignKey support with JSON.

  1. object_id is a CharField (or TextField)
  2. CompositePrimaryKey is stored as a JSON array in object_id
  3. JOINs can be achieved with JSON functions (varies per db backend)

If anyone is interested, I have a proof of concept available on my ​GitHub (it's an out of sync draft right now, I'll submit a proper PR once composite primary keys are merged).

Risks:

  1. What if someone is using a JSON array as the primary key (but it's not a composite primary key)?

Before deserializing the JSON array, we need to check if the content type has a composite primary key or not.

  1. What if the db backend doesn't support JSON functions?

All supported databases support JSON functions.

Notes:

Django admin's LogEntry has its own implementation of "generic foreign keys".
The approach we take with GenericForeignKey should also apply to LogEntry.

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