Billing Development Notes
Models
EventInvoice: FK to events.EventAttendees, stores invoice/reference numbers, invoice/due dates, amount, and currency.EventBillingConfiguration: one-to-one with events.Event, specifying due date, integration type (BillingIntegrations enum), base price(s), and optional price_selector pointing at a registration field name.
Flow (billing/handlers.py)
events.views.EventDetailView.form_valid() calls billing.handlers.handle_event_billing() when the event_billing experimental feature is enabled.handle_event_billing fetches the billing configuration for the event (parent fallback) and resolves the integration provider.- For invoice integration:
- Generates a random invoice number (
generate_invoice_number) and a checksum-protected reference number.
- Computes the amount via
get_selection_price()—either a fixed float or matched to a registration answer by name.
- Creates the
EventInvoice row (with retry recursion on failure).
- Sends an invoice email using
billing/util.send_event_invoice().
- If the price resolves to
0, it sends a free-event confirmation email instead.
Utility Functions
generate_reference_number() implements the 7-3-1 checksum common in Finnish reference numbers.get_selection_price() reads EventRegistrationForm.choice_list to map answers to prices; mismatches raise ValueError.- Email templates live in
templates/billing/. Context merges BILLING_CONTEXT and CONTENT_VARIABLES from settings.
Admin
EventBillingConfigurationAdmin adds a custom URL (/ref_numbers/) to export invoice data as CSV. ref_export renders a button on each row.EventInvoice uses default admin registration.
Extending
- Support additional integrations (e.g., Stripe) by adding new members to
BillingIntegrations and branching in handle_event_billing.
- Persist audit logs (sent emails, retries) to help finance teams troubleshoot.
- Add constraints to prevent deleting an
EventAttendees row that already has invoices unless cascading deletes are expected.