Adding activity logging

Read docs/internal/activity-logging.md first. It carries the pipeline, the file locations, and the reasons. This skill carries the workflow and the gates.

Reference implementation: products/feature_flags/backend/activity_logging.py with its apps.py. Separate-database reference: products/stamphog/backend/activity_logging.py.

Step 1 - Find every write path before you touch the model

The mixin hooks save() and delete(). It does not see QuerySet.update(), bulk_create(), bulk_update(), or raw SQL. A receiver that logs only the API path gives an audit trail that says nobody changed a row a webhook changed.

rg -n "Thing\.objects|Thing\.all_teams" products/<name>/ --type py | rg -v "tests/"
rg -n "\.update\(|bulk_create\(|bulk_update\(" products/<name>/backend --type py

Write the list down: which paths call save() (the mixin covers them) and which do bulk writes (you log those by hand in step 5). Include tasks, Temporal activities, webhook handlers, and management commands.

Step 2 - Model and scope

• Add ModelActivityMixin first in the bases: class Thing(ModelActivityMixin, TeamScopedRootMixin, ...).
• Set activity_logging_on_delete = True only when a hard delete must show in the log.
• Add the class name to ActivityScope in posthog/models/activity_logging/activity_log.py.
• Add the same string to the ActivityScope enum in frontend/src/types.ts.
• Run hogli build:openapi (needs the dev stack) because the API scope filter enum is generated from the Literal.

No migration is needed. The mixin adds no field.

Step 3 - Receiver module

Create products/<name>/backend/activity_logging.py. One @mutable_receiver(model_activity_signal, sender=Thing) per model. The receiver calls changes_between and log_activity; nothing else.

Keep the module import-light. It must not import a viewset, a serializer, or a query runner. ready() imports it at django.setup() in every process.

For a model without a .team foreign key (ProductTeamModel), read organization_id from Team on the main database inside the receiver.

Step 4 - Wire it

• In products/<name>/backend/apps.py ready(): from products.<name>.backend import activity_logging # noqa: F401, PLC0415, with a one-line comment that says why it must connect in every process.
• Add model_activity:products.<name>.backend.activity_logging.<handler> to posthog/test/repo_invariants/setup_receivers_baseline.txt.

A receiver that is not imported in ready() connects only where something else imports the module. That is the silent failure this convention exists to prevent.

Step 5 - Bulk writes

For each bulk write from step 1:

• Read the before-values from the writer database before the update.
• Run the update.
• Build one Change per field that actually changed, for rows whose value changed.
• Call bulk_log_activity (or log_activity for one row) with user=None when no request user exists, and a Trigger that names the job and its id.

Do not wrap a request path in mute_selected_signals(). The flag is process-wide.

Step 6 - Separate-database products only

When the model is routed in products/db_routing.yaml:

• Pass using=router.db_for_write(Thing) to every log_activity and bulk_log_activity call in the product, including the receiver. Without it, the audit row is written before the product row commits and survives its rollback.
• The mixin already pins its before-update read to the writer and reads by primary key without a team filter.

Step 7 - Tune the diff

• Fields a job touches on every run go in signal_exclusions (no row is logged when only they change).
• Bookkeeping fields go in field_exclusions (dropped from the diff).
• Secrets go in field_with_masked_contents (the change is recorded, the values are not).
• User-facing names go in field_name_overrides.

Step 8 - Describer (optional)

defaultDescriber renders "X created / updated / deleted ". Write products/<name>/frontend/activityDescriber.tsx and register it in frontend/src/lib/components/ActivityLog/describers.tsx when the default text does not say what changed in the user's words. Invoke /writing-user-facing-copy before you write the strings.

Step 9 - Tests

Invoke /writing-tests first. Add the tests listed under Tests in the doc, and no more.

Verify

hogli test products/<name>/backend/tests/<file>.py
hogli test posthog/test/repo_invariants/test_startup_import_budget.py
ruff check products/<name>/backend/activity_logging.py posthog/models/activity_logging --fix

Then check the row in a shell: ActivityLog.objects.filter(scope="Thing").order_by("-created_at").first().detail.

Debugging a missing row

Work down this list; each item is a distinct cause.

1. The receiver module is not imported in ready() (check setup_receivers_baseline.txt for the handler name).
2. The write bypassed save() (step 1).
3. Only excluded fields changed (signal_exclusions), or the diff was empty and force_save was not set.
4. ACTIVITY_LOG_TRANSACTION_MANAGEMENT deferred the write to a commit that never came, or to the wrong connection (step 6).
5. The row exists but the reader is outside the entitlement's lookback window, or activity_visibility_restrictions hides it.