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Question

我无法使select_related使用以下配置：

型号：

class Text(models.Model):
    author = models.ForeignKey('authors.Author', 
                               on_delete=models.SET_NULL,
                               blank=True,
                               null=True)

作者模型：

class Author(models.Model):
    name = models.CharField(max_length=200)
    def get_absolute_url(self):
        kwargs = {'pk': self.pk}
        return reverse('author-detail', kwargs=kwargs)

查看

在一种视图中，我使用select_related函数来避免在查询文本作者时碰到数据库，例如：mytext.author：

class TextsViewTest(TestCase):
    def text_view(request,
                 pk,                            
                 template_name='texts/detail.html'):

        source_text = Text.objects.select_related('author').get(pk=pk)
        return render(request, template_name,
                 {
                     'source': source_text,
                 })

测试

根据select_related，在访问Text.author关系时，它不应访问数据库，而在使用以下方法进行测试时：

def test_layout_content_header__uses_prefetched_relationships(self):
    author = Author.objects.create(name="foobar")
    source_text = Text.objects.create(author=author)
    context = {'source': source_text}
    with self.assertNumQueries(0):
        from django.template.loader import render_to_string
        rendered = render_to_string("text/_content_header.html", context)

模板

text/content_header.html：

{% if source.author %} by <em><a href="{{source.author.get_absolute_url}}">{{source.author.name}}</a></em>{% endif %}

输出

./manage test texts.test_views显示匹配：

Creating test database for alias 'default'...
System check identified no issues (0 silenced).
F
======================================================================
FAIL: test_layout_content_header__uses_prefetched_relationships (author.tests.test_views.TextsViewTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/.../text/tests/test_views.py", line 1035, in test_layout_content_header__uses_prefetched_relationships
    source_text.author
  File "/.../lib/python3.6/site-packages/django/test/testcases.py", line 80, in __exit__
    '%d. %s' % (i, query['sql']) for i, query in enumerate(self.captured_queries, start=1)
AssertionError: 1 != 0 : 1 queries executed, 0 expected
Captured queries were:
1. SELECT "authors_author"."id", "authors_author"."name", FROM "authors_author" WHERE "authors_author"."id" = 1

----------------------------------------------------------------------
Ran 1 test in 0.489s

FAILED (failures=1)
Destroying test database for alias 'default'...

有什么想法吗？

Answer 1

您似乎没有在测试中使用视图的代码。尝试将同一查询复制到您的测试中，例如：

context = {'source': Text.objects.select_related('author').get(pk=source_text.pk)}
with self.assertNumQueries(0):
    from django.template.loader import render_to_string
    rendered = render_to_string("text/_content_header.html", context)

或重用视图代码（它似乎在测试用例中声明了，对吧？）

with self.assertNumQueries(1):
    self.text_view(MagicMock(), source_text.pk)

尽管您可能需要指定一些更高级的请求模拟，例如使用RequestFactory