Opened 2 years ago

Closed 2 years ago

#23001 closed Bug (fixed)

Annotation breaks with deferred fields and select_related

Reported by: jarshwah Owned by: Josh Smeaton
Component: Database layer (models, ORM) Version: master
Severity: Normal Keywords:
Cc: Triage Stage: Ready for checkin
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


I've discovered a bug that I think was introduced by:

The problem manifests as annotations being assigned an incorrect value when there are deferred fields and select_related is in use.

Passing Test:

def test_annotate_defer(self):
        qs = Book.objects.annotate(

        rows = [
            (1, "159059725", 447, "The Definitive Guide to Django: Web Development Done Right")
            qs.order_by('pk'), rows,
            lambda r: (, r.isbn, r.page_sum,

Failing Test:

def test_annotate_defer_select_related(self):
        qs = Book.objects.select_related('contact').annotate(

        rows = [
            (1, "159059725", 447, "Adrian Holovaty",
            "The Definitive Guide to Django: Web Development Done Right")
            qs.order_by('pk'), rows,
            lambda r: (, r.isbn, r.page_sum,,

The problem is in the iterator method of django.db.models.query, which results in the aggregate_start variable being off by len(deferred):

if load_fields and not fill_cache:
            # Some fields have been deferred, so we have to initialize
            # via keyword arguments.
            skip = set()
            init_list = []
            for field in fields:
                if not in load_fields:
            model_cls = deferred_class_factory(self.model, skip)
            model_cls = self.model
            init_list = [f.attname for f in fields]

fill_cache is set to true when select_related is in use, which skips to the else block. The else block doesn't take deferred fields into account like the if block does. I'll attempt to patch this by including similar logic in the else block (skipping deferred fields), but I'm not yet sure what else that might affect.

Change History (5)

comment:1 Changed 2 years ago by jarshwah

Needs documentation: unset
Needs tests: unset
Patch needs improvement: unset

Both tests pass on the 1.7 branch.

comment:3 Changed 2 years ago by Tim Graham

Triage Stage: UnreviewedReady for checkin
Type: UncategorizedBug

comment:4 Changed 2 years ago by Josh Smeaton

Owner: changed from jarshwah to Josh Smeaton
Status: newassigned

comment:5 Changed 2 years ago by Anssi Kääriäinen <akaariai@…>

Resolution: fixed
Status: assignedclosed

In 5b0375ec3e7473fcc29c21003fef80c0d0be183f:

Fixed #23001 -- Fixed mixing defer and annotations

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