django 1.6 - get related objects of related objects - django

Question

I have the following three models:
class Region(models.Model):
code = models.IntegerField()
class ReportRequest(models.Model):
# a report can include many regions
regions = models.ManyToManyField(Region)
class Office(models.Model):
# an office belongs to one region
region = models.ForeignKey(Region)
basically, many reports can have many regions, and one region can have many offices.
How can I get all offices related to my report's regions in one query?
I can do this with two queries:
region_pks = reportrequest.regions.values_list('id', flat=True)
offices = Office.objects.filter(region_id__in=region_pks)
but I feel there must be a way to do this in just one query.
I know how to do this if this was a chain of objects connected by ForeignKeys, but ManyToManyField confuses me a bit.
update:
this way Office.objects.filter(region__in=reportrequest.regions) doesn't work.
reportrequest = ReportRequest.objects.first()
print(Office.objects.filter(region__in=reportrequest.regions).all())
Traceback (most recent call last):
File "/Users/9999/_projects/declarator/transparency/transparency/scripts/process_report_requests.py", line 22, in <module>
print(Office.objects.filter(region__in=reportrequest.regions).all())
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/manager.py", line 92, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/query.py", line 691, in filter
return self._filter_or_exclude(False, *args, **kwargs)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/modeltranslation/manager.py", line 338, in _filter_or_exclude
return super(MultilingualQuerySet, self)._filter_or_exclude(negate, *args, **kwargs)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/query.py", line 709, in _filter_or_exclude
clone.query.add_q(Q(*args, **kwargs))
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1287, in add_q
clause, require_inner = self._add_q(where_part, self.used_aliases)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1314, in _add_q
current_negated=current_negated, connector=connector)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1142, in build_filter
value, lookups = self.prepare_lookup_value(value, lookups, can_reuse)
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1047, in prepare_lookup_value
value = value()
File "/Users/9999/.virtualenvs/transparency/lib/python2.7/site-packages/django/db/models/fields/related.py", line 839, in __call__
manager = getattr(self.model, kwargs.pop('manager'))
KeyError: u'manager'

Answer 1

This
offices = Office.objects.filter(region__in=reportrequest.regions.all())