Django TypeError：預期的字符串或緩沖區

Question

將DateField添加到模型中時，有時會彈出一個問題。 我相信將日期字段添加到已經有數據的表中時會發生這種情況。問題是我無法使錯誤消失。 每次我運行遷移時，都會報錯TypeError: expected string or buffer

有沒有辦法強制遷移。 甚至在我從模型中刪除字段，刪除數據庫並刪除遷移之后，都會發生這種情況。 我也嘗試過手動將datestamp輸入數據庫。

我可以解決的唯一方法是創建一個新項目並復制代碼。

我將創建和last_modified添加到處理錯誤的模型中

class Entry(models.Model):
    title = models.CharField(max_length=50, blank=True, null=True)
    start = models.DateField(blank=True, null=True)
    end = models.DateField(blank=True, null=True)

    creation = models.DateField(auto_now_add=True)
    last_modified = models.DateField(auto_now=True)

    def __unicode__(self):
        return self.title

從那以后，我又回到了它工作的時候。

class Entry(models.Model):
    title = models.CharField(max_length=50, blank=True, null=True)
    start = models.DateField(blank=True, null=True)
    end = models.DateField(blank=True, null=True)

    def __unicode__(self):
        return self.title

完全錯誤：

  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/core/management/base.py", line 393, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/core/management/base.py", line 444, in execute
    output = self.handle(*args, **options)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 222, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/migrations/executor.py", line 110, in migrate
    self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/migrations/executor.py", line 148, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/migrations/migration.py", line 115, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 62, in database_forwards
    field,
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 179, in add_field
    self._remake_table(model, create_fields=[field])
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 77, in _remake_table
    self.effective_default(field)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 211, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 710, in get_db_prep_save
    prepared=False)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1322, in get_db_prep_value
    value = self.get_prep_value(value)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1317, in get_prep_value
    return self.to_python(value)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1274, in to_python
    parsed = parse_date(value)
  File "/Users/User/pyProjects/projects/Folder/Env/lib/python2.7/site-packages/django/utils/dateparse.py", line 60, in parse_date
    match = date_re.match(value)
TypeError: expected string or buffer

Answer 1

auto_now和auto_now_add曾引起遷移問題，最好的方法是改為使用默認字段。

from django.utils import timezone

class Entry(models.Model):
    title = models.CharField(max_length=50, blank=True, null=True)
    start = models.DateField(blank=True, null=True)
    end = models.DateField(blank=True, null=True)

    creation = models.DateField(default=timezone.now())
    last_modified = models.DateField(default=timezone.now())

    def __unicode__(self):
        return self.title

我使用時區模塊，如果您的項目知道時區，則首選此模塊。

Answer 2

如果@petkostas提供的解決方案不起作用，請嘗試在模型中使用str而不是unicode

例：

def __str__(self):
        return self.title