在我的 Django 应用程序中，我在 models.py 中有两行使用 ContentType.objects.get():
class Comment (Content):
text = models.CharField(max_length=500)
proposal = models.ForeignKey("Proposal", null=False, related_name="comments")
contentType = ContentType.objects.get(app_label="myapp", model="comment")
class Proposal (Content):
title = models.CharField(max_length=100)
text = models.TextField()
contentType = ContentType.objects.get(app_label="myapp", model="proposal")
当我运行 python manage.py syncdb 甚至 python manage.py shell 时，它们会抛出一个错误 (django.db.utils.ProgrammingError: relation "django_content_type"不存在)。我试过删除并重新创建数据库无济于事。 如果我注释掉这两行，syncdb 工作正常(但这显然会破坏应用程序)。
django.contrib.contenttypes 在我的 INSTALLED_APPS 中。
这是完整的回溯:
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
utility.execute()
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/__init__.py", line 392, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/base.py", line 242, in run_from_argv
self.execute(*args, **options.__dict__)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/base.py", line 284, in execute
self.validate()
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/base.py", line 310, in validate
num_errors = get_validation_errors(s, app)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/core/management/validation.py", line 34, in get_validation_errors
for (app_name, error) in get_app_errors().items():
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/loading.py", line 196, in get_app_errors
self._populate()
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/loading.py", line 75, in _populate
self.load_app(app_name, True)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/loading.py", line 99, in load_app
models = import_module('%s.models' % app_name)
File "/path/to/virtualenv/lib/python3.4/importlib/__init__.py", line 104, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 2231, in _gcd_import
File "<frozen importlib._bootstrap>", line 2214, in _find_and_load
File "<frozen importlib._bootstrap>", line 2203, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 1200, in _load_unlocked
File "<frozen importlib._bootstrap>", line 1129, in _exec
File "<frozen importlib._bootstrap>", line 1448, in exec_module
File "<frozen importlib._bootstrap>", line 321, in _call_with_frames_removed
File "/path/to/django/app/models.py", line 42, in <module>
class Comment (Content):
File "/path/to/django/app/models.py", line 46, in Comment
contentType = ContentType.objects.get(app_label="myapp", model="comment")
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/manager.py", line 151, in get
return self.get_queryset().get(*args, **kwargs)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/query.py", line 301, in get
num = len(clone)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/query.py", line 77, in __len__
self._fetch_all()
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/query.py", line 854, in _fetch_all
self._result_cache = list(self.iterator())
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/query.py", line 220, in iterator
for row in compiler.results_iter():
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/sql/compiler.py", line 709, in results_iter
for rows in self.execute_sql(MULTI):
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/models/sql/compiler.py", line 782, in execute_sql
cursor.execute(sql, params)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/backends/util.py", line 69, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/backends/util.py", line 53, in execute
return self.cursor.execute(sql, params)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/utils.py", line 99, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/utils/six.py", line 535, in reraise
raise value.with_traceback(tb)
File "/path/to/virtualenv/lib/python3.4/site-packages/django/db/backends/util.py", line 53, in execute
return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "django_content_type" does not exist
LINE 1: ..."."app_label", "django_content_type"."model" FROM "django_co...
请您参考如下方法:
我不确定您要做什么，但是您不能像在另一个模型的定义中那样使用模型对象。您要求 Django 在执行任何其他操作之前获取 ContentType 的特定实例 - 甚至在它有机会为 ContentType 创建表之前。您需要 ContentType 的外键。
class Comment (Content):
text = models.CharField(max_length=500)
proposal = models.ForeignKey("Proposal", null=False, related_name="comments")
contentType = models.ForeignKey(ContentType)
假设虽然您实际追求的是一个通用关系，但您还需要为该关系指向的任何类的对象 ID 添加一个字段，以及一个伪字段以简化访问:
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey('contentType', 'object_id')
