Design a Django Model with Signals for Automated Workflows
Generate a Django model with status tracking, custom managers, and pre/post save signals for automated business workflows.
📝 The Prompt
Create a Django model called `[MODEL_NAME]` for a [APPLICATION_CONTEXT] application with associated signals that automate [WORKFLOW_DESCRIPTION].
**Model Definition:**
1. Define the model with these fields: [FIELD_DEFINITIONS] (include field types, constraints, help_text, and db_index where appropriate)
2. Add a `status` field using `TextChoices` with states: [STATUS_CHOICES] (e.g., draft, pending, approved, archived)
3. Include audit fields: `created_at`, `updated_at`, `created_by` (ForeignKey to User)
4. Implement these model methods:
- `clean()` for cross-field validation: [VALIDATION_RULES]
- `__str__()` returning a meaningful representation
- A custom manager method `[MANAGER_METHOD_NAME]` that filters by [FILTER_CRITERIA]
- A property `[COMPUTED_PROPERTY]` that calculates [CALCULATION_LOGIC]
**Signal Implementations:**
1. **`pre_save`**: Before saving, automatically [PRE_SAVE_ACTION] (e.g., generate slug, normalize data, validate state transitions). Prevent invalid status transitions by checking `old_value → new_value` against an allowed transitions map.
2. **`post_save`**: After creation (`created=True`), trigger [POST_CREATE_ACTION] (e.g., send notification, create related records, enqueue async task). After update, [POST_UPDATE_ACTION].
3. **`pre_delete`**: Before deletion, [PRE_DELETE_ACTION] (e.g., soft-delete instead, archive related data, check business rules).
**Deliverables:**
- `models.py` with the model, custom manager, and choices class
- `signals.py` with all signal handlers using the `@receiver` decorator
- `apps.py` with the `ready()` method importing signals
- A migration file or instructions for `makemigrations`
- 3 test cases in `tests/test_signals.py` verifying each signal fires correctly
Follow Django best practices: keep signals thin, use `update_fields` checks to avoid infinite loops, and document signal side effects.
💡 Tips for Better Results
Define your status transition map explicitly in [STATUS_CHOICES] (e.g., 'draft→pending→approved') to get proper state machine validation in pre_save. Always request the update_fields infinite-loop guard — it's the most common Django signal bug. Keep signal handlers thin by delegating to service functions you can test independently.
🎯 Use Cases
Django developers use this when building models that need automated side effects on creation, update, or deletion — such as order processing, content approval, or audit logging workflows.