我不知道是我做错了什么，还是我在项目中使用的一个部件有问题。
基本上，我在一个模型中添加了一个字段，并试图进行迁移。
下面是模型。这个字段是 poster 一。
class Video(models.Model):
title=models.CharField(max_length=500)
description=models.TextField(default="")
creation_date=models.DateTimeField(default=timezone.now)
videofile=models.FileField(upload_to='videos/', null=True, verbose_name="")
poster=models.ImageField(upload_to='video/thumbnails', null=True, verbose_name="")
tags = TaggableManager()
actions = ['delete']
def __str__(self):
return self.title + ": " + str(self.videofile)
...
这是模型中唯一改变的东西。让我们进行迁移。
(app-web) selfishman@user-desktop:~/sites/app-web/app$ python manage.py makemigrations
Migrations for 'video_uploader':
video_uploader/migrations/0007_video_poster.py
- Add field poster to video
到目前为止，一切正常。让我们尝试应用迁移。
(app-web) user@user-desktop:~/sites/app-web/app$ python manage.py migrate video_uploader
Operations to perform:
Apply all migrations: video_uploader
Running migrations:
Applying video_uploader.0002_video_creation_date...Traceback (most recent call last):
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 85, in _execute
return self.cursor.execute(sql, params)
psycopg2.errors.DuplicateColumn: column "creation_date" of relation "video_uploader_video" already exists
有其余的回溯。
上面的异常是下面异常的直接原因。
Traceback (most recent call last):
File "manage.py", line 20, in <module>
execute_from_command_line(sys.argv)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/__init__.py", line 381, in execute_from_command_line
utility.execute()
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/__init__.py", line 375, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/base.py", line 316, in run_from_argv
self.execute(*args, **cmd_options)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/base.py", line 353, in execute
output = self.handle(*args, **options)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/base.py", line 83, in wrapped
res = handle_func(*args, **kwargs)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/core/managemen
t/commands/migrate.py", line 203, in handle
fake_initial=fake_initial,
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/migrations/
executor.py", line 117, in migrate
state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/migrations/
executor.py", line 147, in _migrate_all_forwards
state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/migrations/
executor.py", line 244, in apply_migration
state = migration.apply(state, schema_editor)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/migrations/
migration.py", line 124, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/migrations/
operations/fields.py", line 84, in database_forwards
field,
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ba
se/schema.py", line 435, in add_field
self.execute(sql, params)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ba
se/schema.py", line 133, in execute
cursor.execute(sql, params)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 100, in execute
return super().execute(sql, params)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 68, in execute
return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 77, in _execute_with_wrappers
return executor(sql, params, many, context)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 85, in _execute
return self.cursor.execute(sql, params)
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/utils.py",
line 89, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/home/user/miniconda3/envs/app-web/lib/python3.7/site-packages/django/db/backends/ut
ils.py", line 85, in _execute
return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: column "creation_date" of relation "video_uploader_video" already exists
这是被创建的迁移。
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
('video_uploader', '0006_video_description'),
]
operations = [
migrations.AddField(
model_name='video',
name='poster',
field=models.ImageField(null=True, upload_to='video/thumbnails', verbose_name=''),
),
]
谁能告诉我这是怎么回事？我使用的是Postgres 12。当我运行测试，并从头开始创建一个（SQLite）DB时，没有出现这样的错误。
感谢任何帮助。
P.S.当涉及到Django迁移和PostgresPsycopg2时，我们已经看到了不少不一致的地方。不知道是配置的问题还是版本依赖的问题。
你创建了一个新的迁移，它被命名为
0007_video_poster
但当你运行迁移时，它却在运行以下内容
0002_video_creation_date
而这是在尝试创建一个新的列，名为 creation_date 然而这已经存在了。
你得到了不一致的结果，因为django认为之前的迁移没有被应用，所以它试图应用它们。
最简单的方法是 flush 数据库（确保首先导出您可能需要的任何数据），使用
python manage.py flush
这将重置数据库，然后你可以正常运行迁移，应该可以正常工作。
否则，如果你想执行你刚刚创建的迁移，即。0007_video_poster
你可以运行以下命令
python manage.py migrate video_uploader 0007_video_poster