python - '' 中的未知列 'field list'。 Django

Question

我正在使用 Django 1.9 和 MySQL。我想重命名模型中的字段。让我们看看 Django getting started tutorial 中的模型 Choice .

class Choice(models.Model):
  question = models.ForeignKey(Question)
  choice_text = models.CharField(max_length = 200)
  votes = models.IntegerField(default=0)

因此，我想将 votes 字段重命名为 votes_count。我创建了一个空迁移并添加到以下行的操作中:

migrations.RenameField (
    model_name='choice',
    old_name='votes',
    new_name='votes_count',
),

在python manage.py migrate之后，数据库表中的字段被重命名了。但是当我尝试使用这个模型时

def vote(request, question_id):
  question = get_object_or_404(Question, pk=question_id);
  try:
    selected = question.choice_set.get(pk=request.POST['choice'])
  except (KeyError, Choice.DoesNotExist):
    return render(request, 'polls/detail.html', {
      'question':question,
      'error_message':"You didn't select a choice."
    })
  else:
    selected.votes_count += 1
    selected.save()
    return HttpResponseRedirect(reverse('polls:results', args=(question_id)))

我得到了:

Unknown column 'polls_choice.votes' in 'field list

    Traceback:

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/utils.py" in execute
      64.                 return self.cursor.execute(sql, params)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/mysql/base.py" in execute
      112.             return self.cursor.execute(query, args)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in execute
      226.             self.errorhandler(self, exc, value)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/connections.py" in defaulterrorhandler
      36.         raise errorvalue

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in execute
      217.             res = self._query(query)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in
_query
      378.         rowcount = self._do_query(q)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in
_do_query
      341.         db.query(q)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/connections.py" in query
      280.             _mysql.connection.query(self, query)

    The above exception ((1054, "Unknown column 'polls_choice.votes' in 'field list'")) was the direct cause of the following exception:

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/core/handlers/base.py" in get_response
      149.                     response = self.process_exception_by_middleware(e, request)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/core/handlers/base.py" in get_response
      147.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)

    File "./polls/views.py" in vote
      23.     selected = question.choice_set.get(pk=request.POST['choice'])

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/manager.py" in manager_method
      122.                 return getattr(self.get_queryset(), name)(*args, **kwargs)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/query.py" in get
      381.         num = len(clone)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/query.py" in __len__
      240.         self._fetch_all()

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/query.py" in _fetch_all
      1074.             self._result_cache = list(self.iterator())

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/query.py" in __iter__
      52.         results = compiler.execute_sql()

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/models/sql/compiler.py" in execute_sql
      848.             cursor.execute(sql, params)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/utils.py" in execute
      79.             return super(CursorDebugWrapper, self).execute(sql, params)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/utils.py" in execute
      64.                 return self.cursor.execute(sql, params)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/utils.py" in
__exit__
      95.                 six.reraise(dj_exc_type, dj_exc_value, traceback)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/utils/six.py" in reraise
      685.             raise value.with_traceback(tb)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/utils.py" in execute
      64.                 return self.cursor.execute(sql, params)

    File "/home/verdigo/venv/lib/python3.4/site-packages/django/db/backends/mysql/base.py" in execute
      112.             return self.cursor.execute(query, args)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in execute
      226.             self.errorhandler(self, exc, value)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/connections.py" in defaulterrorhandler
      36.         raise errorvalue

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in execute
      217.             res = self._query(query)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in
_query
      378.         rowcount = self._do_query(q)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/cursors.py" in
_do_query
      341.         db.query(q)

    File "/home/verdigo/venv/lib/python3.4/site-packages/MySQLdb/connections.py" in query
      280.             _mysql.connection.query(self, query)

    Exception Type: OperationalError at /polls/1/vote/
    Exception Value: (1054, "Unknown column 'polls_choice.votes' in 'field list'")

Answer 1

看起来您创建并运行了一个迁移以将模型字段从 votes 重命名为 votes_count，但并未同时更新模型。

当 Django 尝试从数据库中获取模型时，它会尝试选择 votes 列，因为您的模型中仍然有一个 votes 字段，并且您会收到错误消息，因为该列没有数据库中不存在。

通常不需要创建手动迁移。通常，您会重命名模型字段，运行 makemigrations，然后运行 ​​migrate。让 Django 创建迁移的好处是您可以确信在运行迁移后数据库与您的模型同步。