text: from djmodels.core.exceptions import FieldError
  from djmodels.db.models import Count, F, Max
  from djmodels.test import TestCase
  
  from .models import A, B, Bar, D, DataPoint, Foo, RelatedPoint
  
  
  class SimpleTest(TestCase):
      def setUp(self):
          self.a1 = A.objects.create()
          self.a2 = A.objects.create()
          for x in range(20):
              B.objects.create(a=self.a1)
              D.objects.create(a=self.a1)
  
      def test_nonempty_update(self):
          """
          Update changes the right number of rows for a nonempty queryset
          """
          num_updated = self.a1.b_set.update(y=100)
          self.assertEqual(num_updated, 20)
          cnt = B.objects.filter(y=100).count()
          self.assertEqual(cnt, 20)
  
      def test_empty_update(self):
          """
          Update changes the right number of rows for an empty queryset
          """
          num_updated = self.a2.b_set.update(y=100)
          self.assertEqual(num_updated, 0)
          cnt = B.objects.filter(y=100).count()
          self.assertEqual(cnt, 0)
  
      def test_nonempty_update_with_inheritance(self):
          """
          Update changes the right number of rows for an empty queryset
          when the update affects only a base table
          """
          num_updated = self.a1.d_set.update(y=100)
          self.assertEqual(num_updated, 20)
          cnt = D.objects.filter(y=100).count()
          self.assertEqual(cnt, 20)
  
      def test_empty_update_with_inheritance(self):
          """
          Update changes the right number of rows for an empty queryset
          when the update affects only a base table
          """
          num_updated = self.a2.d_set.update(y=100)
          self.assertEqual(num_updated, 0)
          cnt = D.objects.filter(y=100).count()
          self.assertEqual(cnt, 0)
  
      def test_foreign_key_update_with_id(self):
          """
          Update works using <field>_id for foreign keys
          """
          num_updated = self.a1.d_set.update(a_id=self.a2)
          self.assertEqual(num_updated, 20)
          self.assertEqual(self.a2.d_set.count(), 20)
  
  
  class AdvancedTests(TestCase):
  
      def setUp(self):
          self.d0 = DataPoint.objects.create(name="d0", value="apple")
          self.d2 = DataPoint.objects.create(name="d2", value="banana")
          self.d3 = DataPoint.objects.create(name="d3", value="banana")
          self.r1 = RelatedPoint.objects.create(name="r1", data=self.d3)
  
      def test_update(self):
          """
          Objects are updated by first filtering the candidates into a queryset
          and then calling the update() method. It executes immediately and
          returns nothing.
          """
          resp = DataPoint.objects.filter(value="apple").update(name="d1")
          self.assertEqual(resp, 1)
          resp = DataPoint.objects.filter(value="apple")
          self.assertEqual(list(resp), [self.d0])
  
      def test_update_multiple_objects(self):
          """
          We can update multiple objects at once.
          """
          resp = DataPoint.objects.filter(value='banana').update(value='pineapple')
          self.assertEqual(resp, 2)
          self.assertEqual(DataPoint.objects.get(name="d2").value, 'pineapple')
  
      def test_update_fk(self):
          """
          Foreign key fields can also be updated, although you can only update
          the object referred to, not anything inside the related object.
          """
          resp = RelatedPoint.objects.filter(name="r1").update(data=self.d0)
          self.assertEqual(resp, 1)
          resp = RelatedPoint.objects.filter(data__name="d0")
          self.assertEqual(list(resp), [self.r1])
  
      def test_update_multiple_fields(self):
          """
          Multiple fields can be updated at once
          """
          resp = DataPoint.objects.filter(value="apple").update(
              value="fruit", another_value="peach")
          self.assertEqual(resp, 1)
          d = DataPoint.objects.get(name="d0")
          self.assertEqual(d.value, 'fruit')
          self.assertEqual(d.another_value, 'peach')
  
      def test_update_all(self):
          """
          In the rare case you want to update every instance of a model, update()
          is also a manager method.
          """
          self.assertEqual(DataPoint.objects.update(value='thing'), 3)
          resp = DataPoint.objects.values('value').distinct()
          self.assertEqual(list(resp), [{'value': 'thing'}])
  
      def test_update_slice_fail(self):
          """
          We do not support update on already sliced query sets.
          """
          method = DataPoint.objects.all()[:2].update
          msg = 'Cannot update a query once a slice has been taken.'
          with self.assertRaisesMessage(AssertionError, msg):
              method(another_value='another thing')
  
      def test_update_respects_to_field(self):
          """
          Update of an FK field which specifies a to_field works.
          """
          a_foo = Foo.objects.create(target='aaa')
          b_foo = Foo.objects.create(target='bbb')
          bar = Bar.objects.create(foo=a_foo)
          self.assertEqual(bar.foo_id, a_foo.target)
          bar_qs = Bar.objects.filter(pk=bar.pk)
          self.assertEqual(bar_qs[0].foo_id, a_foo.target)
          bar_qs.update(foo=b_foo)
          self.assertEqual(bar_qs[0].foo_id, b_foo.target)
  
      def test_update_m2m_field(self):
          msg = (
              'Cannot update model field '
              '<djmodels.db.models.fields.related.ManyToManyField: m2m_foo> '
              '(only non-relations and foreign keys permitted).'
          )
          with self.assertRaisesMessage(FieldError, msg):
              Bar.objects.update(m2m_foo='whatever')
  
      def test_update_annotated_queryset(self):
          """
          Update of a queryset that's been annotated.
          """
          # Trivial annotated update
          qs = DataPoint.objects.annotate(alias=F('value'))
          self.assertEqual(qs.update(another_value='foo'), 3)
          # Update where annotation is used for filtering
          qs = DataPoint.objects.annotate(alias=F('value')).filter(alias='apple')
          self.assertEqual(qs.update(another_value='foo'), 1)
          # Update where annotation is used in update parameters
          qs = DataPoint.objects.annotate(alias=F('value'))
          self.assertEqual(qs.update(another_value=F('alias')), 3)
          # Update where aggregation annotation is used in update parameters
          qs = DataPoint.objects.annotate(max=Max('value'))
          with self.assertRaisesMessage(FieldError, 'Aggregate functions are not allowed in this query'):
              qs.update(another_value=F('max'))
  
      def test_update_annotated_multi_table_queryset(self):
          """
          Update of a queryset that's been annotated and involves multiple tables.
          """
          # Trivial annotated update
          qs = DataPoint.objects.annotate(related_count=Count('relatedpoint'))
          self.assertEqual(qs.update(value='Foo'), 3)
          # Update where annotation is used for filtering
          qs = DataPoint.objects.annotate(related_count=Count('relatedpoint'))
          self.assertEqual(qs.filter(related_count=1).update(value='Foo'), 1)
          # Update where annotation is used in update parameters
          # #26539 - This isn't forbidden but also doesn't generate proper SQL
          # qs = RelatedPoint.objects.annotate(data_name=F('data__name'))
          # updated = qs.update(name=F('data_name'))
          # self.assertEqual(updated, 1)
          # Update where aggregation annotation is used in update parameters
          qs = RelatedPoint.objects.annotate(max=Max('data__value'))
          with self.assertRaisesMessage(FieldError, 'Aggregate functions are not allowed in this query'):
              qs.update(name=F('max'))
  