How to Get Foreign Keys Horribly Wrong

10 months ago

Foreign keys are constraints that span multiple relations, making them harder to enforce.
Common pitfalls and optimizations related to foreign keys include handling migrations, locking, and indexing.
Django's `unique_together` is deprecated; use `UniqueConstraint` instead.
Foreign keys implicitly create indexes unless `db_index=False` is set.
Partial indexes can significantly reduce index size by excluding null values.
Concurrent index operations (`CREATE INDEX CONCURRENTLY`, `DROP INDEX CONCURRENTLY`) minimize locking in live systems.
Use `select_for_update(of=('self',))` to avoid locking related tables unnecessarily.
Set `no_key=True` in `select_for_update` to allow referencing objects to be created without blocking.
Always check generated SQL in migrations to avoid unintended side effects.
Order migration operations carefully to minimize downtime and ensure consistency.

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