dumpdata crashes on querysets with prefetch_related().

[Andrea F]

The ./manage.py dumpdata management command calls iterator() on the QuerySets of the models, but it does not pass chunk_size(​https://github.com/django/django/blob/main/django/core/management/commands/dumpdata.py#L222). On model QuerySets that include prefetch_related, this now (with 5.0) causes this error while running dumpdata:

CommandError: Unable to serialize database: chunk_size must be provided when using QuerySet.iterator() after prefetch_related().

Proposed fix is to pass a suitable chunk_size parameter to iterator() within handle() in dumpdata.py.

[Mariusz Felisiak]

Thanks for the report. Does the following patch work for you?

django/core/management/commands/dumpdata.py

@@ -219 +219 @@
                     if count_only:
                         yield queryset.order_by().count()
                     else:
-                        yield from queryset.iterator()
+                        chunk_size = (
+                            2000 if queryset._prefetch_related_lookups else None
+                        )
+                        yield from queryset.iterator(chunk_size=chunk_size)
 
         try:
             self.stdout.ending = None

Regression in 139135627650ed6aaaf4c755b82c3bd43f2b8f51 (#29984).

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In 38eaf2f2:

Fixed #35159 -- Fixed dumpdata crash when base querysets use prefetch_related().

Regression in 139135627650ed6aaaf4c755b82c3bd43f2b8f51
following deprecation in edbf930287cb72e9afab1f7208c24b1146b0c4ec.

Thanks Andrea F for the report.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7453d6a:

[5.0.x] Fixed #35159 -- Fixed dumpdata crash when base querysets use prefetch_related().

Regression in 139135627650ed6aaaf4c755b82c3bd43f2b8f51
following deprecation in edbf930287cb72e9afab1f7208c24b1146b0c4ec.

Thanks Andrea F for the report.
Backport of 38eaf2f21a2398a8dd8444f6df3723898cb5fe2a from main