Select 相关执行查询

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

在视图中，我使用 select_related 函数来避免在查询文本作者时访问数据库，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 它在访问 Text.author 关系时不应该访问数据库，但是在测试它时：

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 显示命中：

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

看起来您没有在测试中使用您的视图代码。尝试将相同的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)

或者重用视图代码（好像是在Test Case里声明的吧？）

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

尽管您可能需要指定更高级的请求模拟，例如使用 RequestFactory

Select 相关执行查询

Select related executes queries

django

django-testing

django-select-related

django-2.1

型号：

查看

测试

模板

输出