为什么我的数据库会抛出一个错误？

Question

在做Django教程时，我试图通过管理站点访问我的应用程序，并得到以下错误：

DatabaseError at /admin/polls/poll/ (1054, "Unknown column 'polls_poll.question' in 'field list'")

我最初将模型设置为使用问题类，而错误地使用了教程的1.6版本，但切换到1.54版本，不得不将我的问题类重命名为轮询。然后，我重新生成了数据库。我正在使用MySQL。

现在，每次我从管理站点点击“轮询”，它都会抛出上面的错误。

我尝试过刷新我的数据库和重新同步，但这是行不通的。

下面是我的models.py代码：

from django.db import models
import datetime
from django.utils import timezone

class Poll(models.Model):
    question = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

    def __unicode__(self): 
        return self.question

    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

class Choice(models.Model):

    poll = models.ForeignKey(Poll)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

    def __unicode__(self):
        return self.choice_text

以下是完整的回溯：

Internal Server Error: /admin/polls/poll/
Traceback (most recent call last):
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/core/handlers/base.py", line 115, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/contrib/admin/options.py", line 372, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/utils/decorators.py", line 91, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/views/decorators/cache.py", line 89, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/contrib/admin/sites.py", line 202, in inner
    return view(request, *args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/utils/decorators.py", line 25, in _wrapper
    return bound_func(*args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/utils/decorators.py", line 91, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/utils/decorators.py", line 21, in bound_func
    return func(self, *args2, **kwargs2)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/contrib/admin/options.py", line 1285, in changelist_view
    'selection_note': _('0 of %(cnt)s selected') % {'cnt': len(cl.result_list)},
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/models/query.py", line 106, in __len__
    self._result_cache = list(self.iterator())
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/models/query.py", line 317, in iterator
    for row in compiler.results_iter():
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 775, in results_iter
    for rows in self.execute_sql(MULTI):
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 840, in execute_sql
    cursor.execute(sql, params)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/backends/util.py", line 41, in execute
    return self.cursor.execute(sql, params)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 128, in execute
    six.reraise(utils.DatabaseError, utils.DatabaseError(*tuple(e.args)), sys.exc_info()[2])
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 120, in execute
    return self.cursor.execute(query, args)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/MySQLdb/cursors.py", line 201, in execute
    self.errorhandler(self, exc, value)
  File "/Users/MyClean/anaconda/lib/python2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
DatabaseError: (1054, "Unknown column 'polls_poll.question' in 'field list'")

Answer 1

Django的syncdb命令只创建不存在的表。因此，如果您以前已经用不同版本的模型同步过数据库，那么字段名中的任何更改都不会出现在数据库表中。

若要验证，请使用mysql客户端检查polls_poll表。

mysql> DESCRIBE polls_poll;

您可能会看到缺少question字段。

正如注释中所建议的那样，您可以删除整个数据库，但较少的侵入性解决方案只是删除polls_poll表并再次运行syncdb。

mysql> DROP TABLE polls_poll;
$ manage.py syncdb

当然，这将删除所有与投票相关的数据。