Discounts

Plata comes with a discount implementation which already implements a wide range of possible discounting strategies. Several factors decide whether a certain discount is active:

• Its is_active flag.
• The validity period, determined by two dates, valid_from and valid_until.
• The number of allowed uses, allowed_uses. An usage example is limiting a discount to the first ten customers using it.

Plata knows three distinct discount types:

• An amount discount (given with tax included or excluded) which is applied to the subtotal. This type reduces the subtotal, the total and the tax amount.
• A percentage discount which is applied to the subtotal. Like the aforementioned amount type, this type reduces the subtotal, the total and the tax amount.
• A discount code usable as a means of payment. This discount type only leads to a reduced total and does not change the subtotal or the tax amount.

Discounts should not always be applicable to all products which can be bought. Because Plata does not come with a product model it also does not come with many strategies for selecting eligible products.

Bundled strategies are:

• all: All products are eligible.
• exclude_sale: Order items which have their is_sale flag set to True are excluded from discounting.

It’s quite easy to add additional strategies. If you have a category model and only want to allow products from a set of categories for discounting, that’s the code you need:

from django import forms
from django.db.models import Q
from django.utils.translation import ugettext_lazy as _
from plata.discount.models import DiscountBase
from myapp.models import Category

DiscountBase.CONFIG_OPTIONS.append(('only_categories', {
    'title': _('Only products from selected categories'),
    'form_fields': [
        ('categories', forms.ModelMultipleChoiceField(
            Category.objects.all(),
            label=_('categories'),
            required=True,
            )),
        ],
    'product_query': lambda categories: Q(categories__in=categories),
    }))

A different requirement might be that discounts can only be applied if a product will be bought several times (granted, that’s a bit a stupid idea but it demonstrates how eligible products can be determined by their cart status):

from django import forms
from django.db.models import Q
from django.utils.translation import ugettext_lazy as _
from plata.discount.models import DiscountBase
from myapp.models import Category

DiscountBase.CONFIG_OPTIONS.append(('only_multiple', {
    'title': _('Only products which will be bought several times'),
    'orderitem_query': lambda **values: Q(quantity__gt=1),
    }))

Discounts are configured with the following variables:

• The key, given as first argument in the (key, configuration) tuple.
• title: A human-readable title.
• form_fields: A list of (field_name, field_instance) form fields which will be shown in the Django administration. Note: The fields are only visible after saving the discount once.
• product_query: The values from the form fields above will be passed as keyword arguments, the return value is passed to a filter() call on the product model queryset.
• orderitem_query: The values frmo the form fields above will be passed as keyword arguments, the return value is passed to a filter() call on the order items queryset.

form_fields is optional, one of product_query and orderitem_query should always be provided. This is not enforced by the code however.