Django:重复的键值违反了唯一约束

Question

我有一个笑话模型：

class Joke(models.Model):
...
    date_created = models.DateTimeField(default=datetime.now, blank=True)
    date_modified = models.DateTimeField(default=datetime.now, blank=True)
    creator = models.OneToOneField(User, default=1)

现在，当我试图迁移最后一行时，我得到了错误。基本上，我想将一个用户链接到Joke对象，因为我已经有了一个数据库，所以我希望默认值为1，这是管理员用户的id(我检查过了...).Makemigrations工作正常，但是当我尝试迁移时，我得到了这个:

Operations to perform:
  Apply all migrations: jokes_app, sessions, contenttypes, auth, taggit, default, admin
Running migrations:
  Rendering model states... DONE
  Applying jokes_app.0008_auto_20160723_1559...Traceback (most recent call last):
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.IntegrityError: duplicate key value violates unique constraint "jokes_app_joke_creator_id_key"
DETAIL:  Key (creator_id)=(1) already exists.


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 "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/core/management/__init__.py", line 345, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/core/management/base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/core/management/base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 200, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/migrations/executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/migrations/executor.py", line 198, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/migrations/migration.py", line 123, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/migrations/operations/fields.py", line 201, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 482, in alter_field
    old_db_params, new_db_params, strict)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/postgresql/schema.py", line 110, in _alter_field
    new_db_params, strict,
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 644, in _alter_field
    [new_default],
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 110, in execute
    cursor.execute(sql, params)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/utils.py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/home/antoni4040/Documents/Jokes_Website/django-jokes/venv/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.IntegrityError: duplicate key value violates unique constraint "jokes_app_joke_creator_id_key"
DETAIL:  Key (creator_id)=(1) already exists.

我真的不明白怎么了。有什么想法吗？

Answer 1

正如它的名字所说，OneToOne字段强制执行一对一的关系，这在您的情况下意味着一个用户可以创建一个并且只有一个笑话——绝对不是您想要的。改用ForeignKey：

    creator = models.ForeignKey(User, default=1, on_delete=models.SET_DEFAULT)