尝试将数据添加到数据库时，我在Django管理员中遇到“完整性错误”。

追溯如下：

  Environment:


  Request Method: POST
  Request URL: http://127.0.0.1:8000/site/admin/SilverInningsHelpline/classified/add/

  Django Version: 1.6.4
  Python Version: 2.7.3
  Installed Applications:
  ('django_admin_bootstrapped.bootstrap3',
   'django_admin_bootstrapped',
   'django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',
   'SilverInningsHelpline',
   'south')
  Installed Middleware:
  ('django.contrib.sessions.middleware.SessionMiddleware',
   'django.middleware.common.CommonMiddleware',
   'django.middleware.csrf.CsrfViewMiddleware',
   'django.contrib.auth.middleware.AuthenticationMiddleware',
   'django.contrib.messages.middleware.MessageMiddleware',
   'django.middleware.clickjacking.XFrameOptionsMiddleware')


  Traceback:
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
    114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in wrapper
    432.                 return self.admin_site.admin_view(view)(*args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
    99.                     response = view_func(request, *args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
    52.         response = view_func(request, *args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
    198.             return view(request, *args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapper
    29.             return bound_func(*args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
    99.                     response = view_func(request, *args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/utils/decorators.py" in bound_func
    25.                 return func(self, *args2, **kwargs2)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/transaction.py" in inner
    371.                 return func(*args, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in add_view
    1131.                 self.save_model(request, new_object, form, False)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in save_model
    860.         obj.save()
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/base.py" in save
    545.                        force_update=force_update, update_fields=update_fields)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/base.py" in save_base
    573.             updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/base.py" in _save_table
    654.             result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/base.py" in _do_insert
    687.                                using=using, raw=raw)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/manager.py" in _insert
    232.         return insert_query(self.model, objs, fields, **kwargs)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/query.py" in insert_query
    1511.     return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py" in execute_sql
    903.             cursor.execute(sql, params)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/backends/util.py" in execute
    69.             return super(CursorDebugWrapper, self).execute(sql, params)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/backends/util.py" in execute
    53.                 return self.cursor.execute(sql, params)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/utils.py" in __exit__
    99.                 six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/home/siddharth/SilverInnings/venv/local/lib/python2.7/site-packages/django/db/backends/util.py" in execute
    53.                 return self.cursor.execute(sql, params)

  Exception Type: IntegrityError at /site/admin/SilverInningsHelpline/classified/add/
  Exception Value: null value in column "category_id" violates not-null constraint

我的模型如下：

class Categories(models.Model):
    id = models.AutoField(primary_key=True)
    type = models.CharField(max_length=300)

    def __unicode__(self):
        return self.type


class Subcategory(models.Model):
    id = models.AutoField(primary_key=True)
    parent = models.ForeignKey(Categories)
    name = models.CharField(max_length=300)

    def __unicode__(self):
        return self.name



class Classified(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=256)
    contact_person = models.CharField(max_length=300)
    email = models.CharField(max_length=100)
    address = models.ForeignKey(Address)
    subcategory = models.ForeignKey(Subcategory)
    phone_number = models.BigIntegerField(max_length=20, default=0)
    image = models.ImageField(blank=True, upload_to='dynamic/img/')
    NO = 'NO'
    YES = 'YES'
    APPROVAL = ((NO, 'no'), (YES, 'yes'))
    active = models.CharField(choices=APPROVAL, default=NO, max_length=3)
    verified = models.CharField(choices=APPROVAL, default=NO, max_length=3)

    def __unicode__(self):
        return self.name

当我尝试从Admin进入分类表时，就会出现问题。

从这里尝试解决方案：

IntegrityError：“
city_id”列中的null值违反了非null约束，因为它与我的问题最接近。在该链接上尝试解决方案后，我的表如下所示：

class Categories(models.Model):
    id = models.AutoField(primary_key=True)
    type = models.CharField(max_length=300, unique=True, default='All', null=True)

    def __unicode__(self):
        return self.type


class Subcategory(models.Model):
    id = models.AutoField(primary_key=True)
    parent = models.ForeignKey(Categories, null=True, blank=True, default='All')
    name = models.CharField(max_length=300)

    def __unicode__(self):
        return self.name



class Classified(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=256)
    contact_person = models.CharField(max_length=300)
    email = models.CharField(max_length=100)
    address = models.ForeignKey(Address)
    subcategory = models.ForeignKey(Subcategory)
    phone_number = models.BigIntegerField(max_length=20, default=0)
    image = models.ImageField(blank=True, upload_to='dynamic/img/')
    NO = 'NO'
    YES = 'YES'
    APPROVAL = ((NO, 'no'), (YES, 'yes'))
    active = models.CharField(choices=APPROVAL, default=NO, max_length=3)
    verified = models.CharField(choices=APPROVAL, default=NO, max_length=3)

    def __unicode__(self):
        return self.name

但这并不能解决我的问题，现在我被困住了。