Django migrate ProgrammingError: syntax error at or near ""

Question

我正在练习网站上学习 django (1.9.2)，并使用 psycopg2 学习 postgresql 数据库。我定义了一个具有特定属性 "preview" 的模型，后来完全删除了该属性。尽管已将其删除，但 django 似乎正在引用可能来自缓存或其他内容的旧定义。 makemigrations 命令似乎工作正常，反映了我对模型定义所做的每一个更改，但是一旦我运行 migrate 命令，就会弹出此错误。

(env) D:\Web Workspace\Rat Race Website\ratrace>python manage.py migrate
Operations to perform:
  Apply all migrations: contenttypes, news, polls, auth, sessions, admin
Running migrations:
  Applying news.0003_auto_20160212_1209...Traceback (most recent call last):
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: syntax error at or near "9999999999999"
LINE 1: ...ER TABLE "news_news" ADD COLUMN "preview" varchar(9999999999...
                                                             ^


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

Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\core\mana
gement\__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\core\mana
gement\__init__.py", line 345, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\core\mana
gement\base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\core\mana
gement\base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\core\mana
gement\commands\migrate.py", line 200, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\migrat
ions\executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_ini
tial)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\migrat
ions\executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_
initial)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\migrat
ions\executor.py", line 198, in apply_migration
    state = migration.apply(state, schema_editor)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\migrat
ions\migration.py", line 123, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, projec
t_state)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\migrat
ions\operations\fields.py", line 62, in database_forwards
    field,
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\base\schema.py", line 396, in add_field
    self.execute(sql, params)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\base\schema.py", line 110, in execute
    cursor.execute(sql, params)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\utils.
py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\utils\six
.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "D:\Web Workspace\Rat Race Website\env\lib\site-packages\django\db\backen
ds\utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: syntax error at or near "9999999999999"
LINE 1: ...ER TABLE "news_news" ADD COLUMN "preview" varchar(9999999999...

数据库表是空的，所以我怀疑删除数据库并创建一个新数据库可能暂时解决这个问题，但我想要一个更具体的解决方案，以防将来再次发生删除数据库不是一个选项。

这是模型定义的样子。

from django.db import models

# Create your models here.
class News(models.Model):
    headline = models.CharField(max_length=100)
    content = models.CharField(max_length=100)
    pub_date = models.DateTimeField('date published')
    content_preview = models.CharField(max_length=100, blank=True)
    thumbnail = models.ImageField(upload_to='thumbnails/%Y/%m/%d/', blank=True)
    def __str__(self):
        return self.headline

不再有 "preview" 属性，但 django 似乎没有得到它。

编辑：这是预览字段的定义

preview = CharField(max_length=9999999999999)

它产生了一个错误，说它不能为空，所以我输入了一个一次性默认值 "news preview"。我假设默认值是针对现有条目的。当时大约有5个测试条目。请阅读另一篇 post，我在输入一次性默认值时使用的引号可能是问题的原因。关于 psycopg2 的一些事情不喜欢值上的引号？...这是一个字符串值，所以我想我需要引号。

无论如何，现在我已经清除了预览字段，如何让 django 忘记它曾经存在过？

Answer 1

忽略其他评论和我自己的经验。 . .当您收到此错误时，请进入您的迁移文件夹并删除除 __init__.py 之外的所有内容。您甚至可以删除 __pycache__ 文件夹。然后运行 makemigrations 和 migrate 再次。我认为这应该可以解决问题。

Answer 2

如果您未指定 max_length，则在使 CharField 可为空时也会发生这种情况。

所以解决方案是在您的模型中指定 max_length，然后删除并重新制作有问题的迁移..

这是 described as a bug here。

Django migrate ProgrammingError: syntax error at or near ""

Django migrate ProgrammingError: syntax error at or near ""

python

django

postgresql

syntax-error