Django 迁移数据库 django.db.utils.ProgrammingError：关系“django_site”不存在

Question

为 Django 进行站点升级，现在当我尝试python manage.py makemigrations时将其推送到服务器我收到此错误

(kpsga) sammy@kpsga:~/webapps/kpsga$ python manage.py makemigrations
Traceback (most recent call last):
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.UndefinedTable: relation "django_site" does not exist
LINE 1: ..."django_site"."domain", "django_site"."name" FROM "django_si...
                                                            ^


The above exception was the direct cause of the following exception:
...

File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "/home/sammy/webapps/kpsga/kpsga/urls.py", line 27, in <module>
    path('blog', include('blog.urls')),
...
File "/home/sammy/webapps/kpsga/blog/urls.py", line 2, in <module>
    from blog.views import LatestBlogEntries, blog_archive, blog_entry_by_id, blog_entry
File "/home/sammy/webapps/kpsga/blog/views.py", line 10, in <module>
    class LatestBlogEntries(Feed):
File "/home/sammy/webapps/kpsga/blog/views.py", line 11, in LatestBlogEntries
    current_site = Site.objects.get_current()
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/contrib/sites/models.py", line 58, in get_current
    return self._get_site_by_id(site_id)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/contrib/sites/models.py", line 30, in _get_site_by_id
    site = self.get(pk=site_id)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/query.py", line 425, in get
    num = len(clone)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/query.py", line 269, in __len__
    self._fetch_all()
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/query.py", line 1308, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/query.py", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1156, in execute_sql
    cursor.execute(sql, params)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/backends/utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
File "/home/sammy/webapps/envs/kpsga/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "django_site" does not exist
LINE 1: ..."django_site"."domain", "django_site"."name" FROM "django_si...

尽管我已将这些添加到设置文件中

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',


   
    #additional django
    'django.contrib.sites',
]

SITE_ID = 1

最新课程

class LatestBlogEntries(Feed):
    current_site = Site.objects.get_current()
    title = current_site.name + " - Latest News"
    link = "/news/"
    description = "Latest news and updates from " + current_site.domain
    
    def items(self):
        return BlogEntry.objects.all()[:10]
    def item_title(self, item):
        return item.title
    def item_description(self, item):
        return item.description

Answer 1

ProgrammingError 是一个数据库错误。 这意味着您正在尝试读取的表尚未准备好，因为您尝试在创建之前访问它：

class LatestBlogEntries(Feed):
    current_site = Site.objects.get_current()  <---- this line

您应该使用 post_migrate 信号在独立函数中加载静态 current_site 变量。 文档中有一个例子

如果您发现这种矫枉过正，可以使用以下解决方法：

1. 抓住错误。 这将允许您进行迁移，并且在应用程序下次重新启动时，它将完美地读取对象。

    from django.db import ProgrammingError
    class LatestBlogEntries(Feed):
        try:
            current_site = Site.objects.get_current()
        except ProgrammingError:
            pass

2. 如果未定义，则在 _ init_方法中加载变量。

这通常发生在此操作使用已创建的表建模时，然后清除数据库以从头开始。

Answer 2

您不应在LatestBlogEntries类中调用Site.objects.get_current() 。 它需要进行数据库查找，当您尚未运行初始迁移时，这会导致relation does not exist错误。

您可以使用title和description方法。 这样， Site.objects.get_current()在访问提要时运行，而不是在 Django 启动时运行。

class LatestBlogEntries(Feed):

    def title(self, obj):
        current_site = Site.objects.get_current()
        return current_site.name + " - Latest News"

    link = "/news/"

    def description(self, obj):
        current_site = Site.objects.get_current()
        return "Latest news and updates from " + current_site.domain
    
    def items(self):
        return BlogEntry.objects.all()[:10]
    def item_title(self, item):
        return item.title
    def item_description(self, item):
        return item.description