Image some kind of product-rule which has 2 conditions:
- name are equal
- sku's have partial match, starts with.
The rule model looks like this:
class CreateAndAssignRule(models.Model):
name_equals = models.CharField(max_length=100)
sku_starts_with = models.CharField(max_length=100
Now I want to fetch all of the rules with name Product 1
and match sku sku-b-292
class CreateAndAssignRuleQuerySet(QuerySet):
def filter_by_name_and_sku(self, name, sku):
# We're looking which of the rules have a matching name, and where the rule have a string which is the string of the sku provided.
rules = self.filter(name_equals=name)
approved_ids = []
for rule in rules:
# We're looping through the rules to find out which of them has the beginnings of the sku.
# a sku_starts_with field would contains value eg: 'sku-a' where as the search string would be the full sku 'sku-a-111'. We want to match 'sku-a-111' but not 'sku-b-222'.
if sku.startswith(rule.sku_starts_with):
approved.append(rule.id)
return self.filter(id__in=approved_ids)
although the above works, it's hardly efficient especially as the number of rule is starting to grow a lot.
How can I resolve this with a queryset? Filtering on __startswith
doesn't do the trick as it the reverse.
CodePudding user response:
Filter with:
from django.db.models import F, Value
class CreateAndAssignRuleQuerySet(QuerySet):
def filter_by_name_and_sku(self, name, sku):
return self.alias(
sku=Value(sku)
).filter(
name_equals=name,
sku__startswith=F('sku_starts_with')
)
We thus here inject the sku
in the queryset, and then use this to work with a __startswith
lookup [Django-doc].