Pre-validation

~~~~~~~~~~~~~~

Registrasion's ``InvoiceController`` has a ``validate_allowed_to_pay`` method, which performs all of the pre-payment checks (is the invoice still unpaid and non-void? has the registration been amended?).

If the pre-payment check fails, ``InvoiceController`` will raise a Django ``ValidationError``.

Our the ``demopay`` view from the ``registrasion-demo`` project implements pre-validation like so::

    from registrasion.controllers.invoice import InvoiceController

    from django.core.exceptions import ValidationError

    try:

        invoice.validate_allowed_to_pay()  # Verify that we're allowed to do this.

    except ValidationError as ve:

        messages.error(request, ve.message)

        return REDIRECT_TO_INVOICE  # And display the validation message.

In most cases, you don't engage your actual payment application until after pre-validation is finished, as this gives you an opportunity to bail out if the invoice isn't able to have funds applied to it.

Applying payments

~~~~~~~~~~~~~~~~~

Payments in Registrasion are represented as subclasses of the ``PaymentBase`` model. ``PaymentBase`` looks like this: