#32281: Prefetech Object - to_attr has ambiguous behavior when using a related lookup -----------------------------------------+------------------------ Reporter: talolard | Owner: nobody Type: Uncategorized | Status: new Component: Uncategorized | Version: 3.1 Severity: Normal | Keywords: Triage Stage: Unreviewed | Has patch: 0 Needs documentation: 0 | Needs tests: 0 Patch needs improvement: 0 | Easy pickings: 0 UI/UX: 0 | -----------------------------------------+------------------------ **Code Example** {{{ from django.db.models import Prefetch
p = Prefetch("a_set", to_attr="my_a") assert p.prefetch_to == "my_a" p = Prefetch("b__a_set", to_attr="my_a") assert p.prefetch_to == "my_a", p.prefetch_to }}} That last assertion fails because p.prefetch_to == "b__my_a" **Description and use case** We have a models X, Y and Z Z has a foreign key to Y and Y has a foreign key to Z We'd like to fetch X with all of it's Z's using prefetch related and to be able to set the attribute to "z" But as above, this doesn't seem to work. The [https://github.com/django/django/blob/bb64b99b78a579cb2f6178011a4cf9366e634438/django/db/models/query.py#L1570-L1587 relevant Django code] seems to ignore this use case (or discourage it?) and instead puts to "z" attribute on each "Y" {{{ self.prefetch_to = LOOKUP_SEP.join(lookup.split(LOOKUP_SEP)[:-1] + [to_attr]) }}} ---- I assume "fixing this" is a breaking change, but could we do an explicit parameter for prefetch_to ?At the moment we're setting it manually after creating the prefetch object -- Ticket URL: <https://code.djangoproject.com/ticket/32281> Django <https://code.djangoproject.com/> The Web framework for perfectionists with deadlines. -- You received this message because you are subscribed to the Google Groups "Django updates" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-updates+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-updates/051.d6b5ff5402089001d76cf962f6a3bca1%40djangoproject.com.