10 examples of 'django prefetch_related' in Python

53
def test_m2m_forward(self):
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    with self.assertNumQueries(2):
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        lists = [list(b.authors.all()) for b in Book.objects.prefetch_related('authors')]
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    normal_lists = [list(b.authors.all()) for b in Book.objects.all()]
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    self.assertEqual(lists, normal_lists)

706
@property
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def prefetch_related(self):
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    """
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    With main and attached records, prefetch_related lists can be
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    generated by combining the select_related lists for attached
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    children and prefetch_related lists for all children.
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    """
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    try:
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        self._prefetch_related = self._prefetch_related
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    except AttributeError:
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        att_sr = self.combine_rels_from_children('select_related',
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                                                 self.attached_children)
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        all_pr = self.combine_rels_from_children('prefetch_related')
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        self._prefetch_related = self.combine_lists(all_pr, att_sr)
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    return self._prefetch_related

71
def get_prefetch_queryset(self, instances, queryset=None):
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    if queryset is not None:
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        raise ValueError("Custom queryset can't be used for this lookup.")
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    instance = instances[0]
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    db = self._db or router.db_for_read(type(instance), instance=instance)
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    fieldname = (
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        "object_id"
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        if issubclass(self.through, CommonGenericTaggedItemBase)
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        else "content_object"
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    )
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    fk = self.through._meta.get_field(fieldname)
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    query = {
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        "%s__%s__in"
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        % (self.through.tag_relname(), fk.name): {
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            obj._get_pk_val() for obj in instances
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        }
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    }
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    join_table = self.through._meta.db_table
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    source_col = fk.column
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    connection = connections[db]
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    qn = connection.ops.quote_name
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    qs = (
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        self.get_queryset(query)
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        .using(db)
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        .extra(
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            select={
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                "_prefetch_related_val": "{}.{}".format(
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                    qn(join_table), qn(source_col)
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                )
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            }
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        )
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    )
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    if VERSION < (2, 0):
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        return (
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            qs,
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            attrgetter("_prefetch_related_val"),
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            lambda obj: obj._get_pk_val(),
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            False,
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            self.prefetch_cache_name,
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        )
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    else:
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        return (
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            qs,
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            attrgetter("_prefetch_related_val"),
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            lambda obj: obj._get_pk_val(),
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            False,
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            self.prefetch_cache_name,
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            False,
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        )

249
def test_it_prefetches_foreign_key_relations_from_reverse_side_with_serializer_that_has_source(self):
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    # Need two queries because of prefetch related
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    data = _run_test(TopLevelSerializerWithNestedSerializerWithSource, TopLevel, sql_queries=2)
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    assert len(data) == 1
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    assert len(data[0]['kiddos']) == 3

20
async def test_prefetch_object(self):
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    tournament = await Tournament.create(name="tournament")
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    await Event.create(name="First", tournament=tournament)
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    await Event.create(name="Second", tournament=tournament)
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    tournament_with_filtered = (
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        await Tournament.all()
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        .prefetch_related(Prefetch("events", queryset=Event.filter(name="First")))
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        .first()
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    )
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    tournament = await Tournament.first().prefetch_related("events")
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    self.assertEqual(len(tournament_with_filtered.events), 1)
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    self.assertEqual(len(tournament.events), 2)

24
def get_query_set(self, *args, **kwargs):
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    query = super(PartManager, self).get_query_set(*args, **kwargs)
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    query = query.select_related('designation__description',
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                                 'supplier')
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    query = query.prefetch_related('analogs', 'images')
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    return query

149
async def test_get_m2m_forward_prefetch_related(self):
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    obj1 = await self.model.create(chars="aaa")
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    obj2 = await self.model.create(chars="bbb")
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    await obj1.rel_to.add(obj2)
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    obj2a = await self.model.get(eyedee=obj2.eyedee).prefetch_related("rel_from")
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    self.assertEqual(list(obj2a.rel_from), [obj1])

244
def prefetch_export_runs(queryset_list_or_model):
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    prefetch_args = ['job__provider_tasks__provider', 'job__provider_tasks__formats',
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                     'provider_tasks__tasks__result', 'provider_tasks__tasks__exceptions']
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    if isinstance(queryset_list_or_model, models.query.QuerySet):
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        return queryset_list_or_model.select_related('user').prefetch_related(*prefetch_args)
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    elif isinstance(queryset_list_or_model, list):
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        models.prefetch_related_objects(queryset_list_or_model, *prefetch_args)
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    elif isinstance(queryset_list_or_model, ExportRun):
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        models.prefetch_related_objects([queryset_list_or_model], *prefetch_args)
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    return queryset_list_or_model

235
async def test_prefetch_related_missing_field(self):
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    tournament = await Tournament.create(name="New Tournament")
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    await Event.create(name="Test", tournament_id=tournament.id)
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    with self.assertRaisesRegex(FieldError, "Relation tourn1ment for models.Event not found"):
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        await Event.filter(name="Test").prefetch_related("tourn1ment")

586
def test_remove_after_prefetch(self):
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    a4 = Article.objects.prefetch_related('publications').get(id=self.a4.id)
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    self.assertQuerysetEqual(a4.publications.all(), ['<Publication: Science News>'])
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    a4.publications.remove(self.p2)
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    self.assertQuerysetEqual(a4.publications.all(), [])