Problem with get_children() method when using TreeManager. Wrong result - django-mptt

Question

I have encountered an strange problem with the use of TreeManager
Here is my code:
# other imports
from mptt.models import MPTTModel, TreeForeignKey
from mptt.managers import TreeManager
class SectionManager(TreeManager):
def get_queryset(self):
return super().get_queryset().filter(published=True)
class Section(MPTTModel):
published = models.BooleanField(
default=True,
help_text="If unpublished, this section will show only"
" to editors. Else, it will show for all."
)
objects = TreeManager()
published_objects = SectionManager()
When I test it. I get the following correct results:
# show all objects
Section.objects.count() # result is correct - 65
Section.objects.root_nodes().count() # result is correct - 12
# show published objects, just one is not published.
Section.published_objects.count() # result is correct - 64
Section.published_objects.root_nodes().count() # result is corrct - 12
But one child of the roots is unpublished and it does not show in the results. Here is the test:
for root in Section.objects.root_nodes():
print(f"root_section_{root.id} has {root.get_children().count()} children")
# results ...
root_section_57 has 13 children # correct - 13 items
# ... more results
for root in Section.published_objects.root_nodes():
print(f"root_section_{root.id} has {root.get_children().count()} children")
# results ...
root_section_57 has 13 children # WRONG - should be only 12 children
# ... more results
I may not understand something, or I may have hit a bug??
Any ideas?
NOTE: This issue has been posted on the django-mptt github issues page at: https://github.com/django-mptt/django-mptt/issues/689

Answer 1

https://github.com/django-mptt/django-mptt/blob/master/mptt/managers.py
You override wrong function call. root_nodes() call ._mptt_filter()
#delegate_manager
def root_nodes(self):
"""
Creates a ``QuerySet`` containing root nodes.
"""
return self._mptt_filter(parent=None)
And your _mptt_filter does not got any given qs.
#delegate_manager
def _mptt_filter(self, qs=None, **filters):
"""
Like ``self.filter()``, but translates name-agnostic filters for MPTT
fields.
"""
if qs is None:
qs = self
return qs.filter(**self._translate_lookups(**filters))
Now you need to customized based on your use case.
Hope it can be some help