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Discount: Respect addon grouping in line selection (Z#23220058) (#5782)

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* Discount: Respect addon grouping in line selection (Z#23220058)

* Update src/pretix/base/models/discount.py

Co-authored-by: Richard Schreiber <schreiber@pretix.eu>

---------

Co-authored-by: Richard Schreiber <schreiber@pretix.eu>
This commit is contained in:
Raphael Michel
2026-01-16 15:23:59 +01:00
committed by GitHub
parent efb94265b2
commit 0259899e00
7 changed files with 83 additions and 12 deletions
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46
src/pretix/base/models/discount.py
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@@ -37,7 +37,7 @@ from pretix.base.decimal import round_decimal
from pretix.base.models.base import LoggedModel
PositionInfo = namedtuple('PositionInfo',
['item_id', 'subevent_id', 'subevent_date_from', 'line_price_gross', 'is_addon_to',
['item_id', 'subevent_id', 'subevent_date_from', 'line_price_gross', 'addon_to',
'voucher_discount'])
@@ -279,6 +279,42 @@ class Discount(LoggedModel):
for idx in condition_idx_group:
collect_potential_discounts[idx] = [(self, inf, -1, subevent_id)]
def _addon_idx(self, positions, idx):
"""
If we have the following cart:
- Main product
- 10x Addon product 5€
- Main product
- 10x Addon product 5€
And we have a discount rule that grants "every 10th product is free", people tend to expect
- Main product
- 9x Addon product 5€
- 1x Addon product free
- Main product
- 9x Addon product 5€
- 1x Addon product free
And get confused if they get
- Main product
- 8x Addon product 5€
- 2x Addon product free
- Main product
- 10x Addon product 5€
Even if the result is the same. Therefore, we sort positions in the cart not only by price, but also by their
relative index within their addon group. This is only a heuristic and there are *still* scenarios where the more
unexpected version happens, e.g. if prices are different. We need to accept this as long as discounts work on
cart level and not on addon-group level, but this simple sorting reduces the number of support issues by making
the weird case less likely.
"""
if not positions[idx].addon_to:
return 0
return len([1 for i, p in positions.items() if i < idx and p.addon_to == positions[idx].addon_to])
def _apply_min_count(self, positions, condition_idx_group, benefit_idx_group, result, collect_potential_discounts, subevent_id):
if len(condition_idx_group) < self.condition_min_count:
return
@@ -288,8 +324,8 @@ class Discount(LoggedModel):
if self.benefit_only_apply_to_cheapest_n_matches:
# sort by line_price
condition_idx_group = sorted(condition_idx_group, key=lambda idx: (positions[idx].line_price_gross, -idx))
benefit_idx_group = sorted(benefit_idx_group, key=lambda idx: (positions[idx].line_price_gross, -idx))
condition_idx_group = sorted(condition_idx_group, key=lambda idx: (positions[idx].line_price_gross, self._addon_idx(positions, idx), -idx))
benefit_idx_group = sorted(benefit_idx_group, key=lambda idx: (positions[idx].line_price_gross, self._addon_idx(positions, idx), -idx))
# Prevent over-consuming of items, i.e. if our discount is "buy 2, get 1 free", we only
# want to match multiples of 3
@@ -434,7 +470,7 @@ class Discount(LoggedModel):
for idx, p in positions.items():
subevent_to_idx[p.subevent_id].append(idx)
for v in subevent_to_idx.values():
v.sort(key=lambda idx: positions[idx].line_price_gross)
v.sort(key=lambda idx: (positions[idx].line_price_gross, self._addon_idx(positions, idx)))
subevent_order = sorted(list(subevent_to_idx.keys()), key=lambda s: len(subevent_to_idx[s]), reverse=True)
# Build groups of exactly condition_min_count distinct subevents
@@ -458,7 +494,7 @@ class Discount(LoggedModel):
# Sort the list by prices, then pick one. For "buy 2 get 1 free" we apply a "pick 1 from the start
# and 2 from the end" scheme to optimize price distribution among groups
candidates = sorted(candidates, key=lambda idx: positions[idx].line_price_gross)
candidates = sorted(candidates, key=lambda idx: (positions[idx].line_price_gross, self._addon_idx(positions, idx)))
if len(current_group) < (self.benefit_only_apply_to_cheapest_n_matches or 0):
candidate = candidates[0]
else: