from django.conf import settings
from django.conf.urls import include, url  # For django versions before 2.0
from django.urls import include, path  # For django versions from 2.0 and upif settings.DEBUG:import debug_toolbarurlpatterns = [path('__debug__/', include(debug_toolbar.urls)),] + urlpatterns

MIDDLEWARE = [# ...'debug_toolbar.middleware.DebugToolbarMiddleware',# ...
]
第五步:  在settings.py设置本地IP, debug_toolbar只能在localhost本地测试环境下运行。
INTERNAL_IPS = [# ...'127.0.0.1',# ...
]

class Article(models.Model):"""文章模型"""title = models.CharField('标题', max_length=200, db_index=True)category = models.ForeignKey('Category', verbose_name='分类',
on_delete=models.CASCADE, blank=False, null=False)tags = models.ManyToManyField('Tag', verbose_name='标签集合', blank=True)

def article_list(request):articles = Article.objects.all()return render(request, 'blog/article_list.html',
{'articles': articles, })

<ul>
{% for article in articles %}<li>{{ article.title }} </li><li>{{ article.category.name }}</li><li>{% for tag in article.tags.all %}{{ tag.name }},{% endfor %}</li>
{% endfor %}
</ul>

def article_list(request):articles = Article.objects.all().select_related('category')return render(request, 'blog/article_list.html',
{'articles': articles, })

# 获取id=13的文章对象同时，获取其相关category信息
Article.objects.select_related('category').get(id=13)# 获取id=13的文章对象同时，获取其相关作者名字信息
Article.objects.select_related('author__name').get(id=13)# 获取id=13的文章对象同时，获取其相关category和相关作者名字信息。下面方法等同。
Article.objects.select_related('category', 'author__name').get(id=13)
Article.objects.select_related('category').select_related('author__name').get(id=13)# 使用select_related()可返回所有相关主键信息。all()非必需。
Article.objects.all().select_related()# 获取Article信息同时获取blog信息。filter方法和selected_related方法顺序不重要。
Article.objects.filter(pub_date__gt=timezone.now()).select_related('blog')
Article.objects.select_related('blog').filter(pub_date__gt=timezone.now())

def article_list(request):articles = Article.objects.all().select_related('category').prefecth_related('tags')return render(request, 'blog/article_list.html',
{'articles': articles, })

# 文章列表及每篇文章的tags对象名字信息
Article.objects.all().prefetch_related('tags__name')# 获取id=13的文章对象同时，获取其相关tags信息
Article.objects.prefetch_related('tags').get(id=13)

# 获取文章列表及每篇文章相关的名字以P开头的tags对象信息
Article.objects.all().prefetch_related(Prefetch('tags', queryset=Tag.objects.filter(name__startswith="P"))
)# 文章列表及每篇文章的名字以P开头的tags对象信息, 放在article_p_tag列表
Article.objects.all().prefetch_related(Prefetch('tags', queryset=Tag.objects.filter(name__startswith="P")),
to_attr='article_p_tag'
)