Django migrate AttributeError：'str'对象没有属性'_meta'

Question

在对数据库模式进行了一些广泛的更改后，我运行了 makemigrations。它成功创建了迁移。但随后迁移失败：

AttributeError: 'str' object has no attribute '_meta'

这是我更改的代码。我将 Hardskills 的多对多模型从一张表拆分为 2 个不同的用户和作业表。

最初的

class Hardskills(models.Model):
    user = models.ManyToManyField(User, related_name="user_hs",through="HardskillsProfile")
    job = models.ManyToManyField(Job, related_name="job_hs",through="HardskillsProfile")
    hardskills = models.CharField(max_length=100, db_index=True)

    def __str__(self):
        return self.hardskills
    

class HardskillsProfile(models.Model):
    """Through Model for Many to Many relationship for user/jobs and hardskills"""
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="user",null=True)
    job = models.ForeignKey(Job, on_delete=models.CASCADE, related_name="job",null=True)
    hardskills = models.ForeignKey(Hardskills, on_delete=models.CASCADE)

修改后最终结果

from attributes.models import Category
from django.contrib.auth.models import User
from content.models import Job
from django.db import models

class Hardskills(models.Model):
    user = models.ManyToManyField(User, related_name="user_hs",through="UserHardskillsProfile")
    job = models.ManyToManyField(Job, related_name="job_hs",through="JobHardskillsProfile")
    hardskills = models.CharField(max_length=100, db_index=True)

    def __str__(self):
        return self.hardskills
    

class UserHardskillsProfile(models.Model):
    """Through Model for Many to Many relationship for user and hardskills"""
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="user",null=True)
    hardskills = models.ForeignKey(Hardskills, on_delete=models.CASCADE)

class JobHardskillsProfile(models.Model):
    """Through Model for Many to Many relationship for user/jobs and hardskills"""
    job = models.ForeignKey(Job, on_delete=models.CASCADE, related_name="job",null=True)
    hardskills = models.ForeignKey(Hardskills, on_delete=models.CASCADE)

错误日志

Operations to perform:
  Synchronize unmigrated apps: messages, rest_framework, staticfiles
  Apply all migrations: accounts, admin, attributes, auth, authtoken, content, contenttypes, data, interactions, scoring, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
Running migrations:
  Applying scoring.0017_auto_20201224_1023...Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    main()
  File "manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/base.py", line 330, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/base.py", line 371, in execute
    output = self.handle(*args, **options)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/base.py", line 85, in wrapped
    res = handle_func(*args, **kwargs)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/core/management/commands/migrate.py", line 245, in handle
    fake_initial=fake_initial,
  File "/home/yk09/miniconda3/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/yk09/miniconda3/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/yk09/miniconda3/lib/python3.7/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/yk09/miniconda3/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/yk09/miniconda3/lib/python3.7/site-packages/django/db/migrations/operations/fields.py", line 236, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/db/backends/sqlite3/schema.py", line 138, in alter_field
    super().alter_field(model, old_field, new_field, strict=strict)
  File "/home/yk09/miniconda3/lib/python3.7/site-packages/django/db/backends/base/schema.py", line 555, in alter_field
    old_field.remote_field.through._meta.auto_created and
AttributeError: 'str' object has no attribute '_meta'

有人可以建议吗？如果我的问题不清楚，也请告诉我:)

Answer 1

迁移文件中scoring.0017_auto_20201224_1023...会有操作列表。您可以在其中找到删除模型迁移。

将其移动到迁移列表的末尾，例如

从

    [
    ...    
    migrations.DeleteModel(
        name='HardskillsProfile',
    ),
    migrations.AlterField(...),
    ...
    ]

到

    [
    ...
    migrations.DeleteModel(
        name='HardskillsProfile',
    ],

然后迁移。

通过这张票得到了这个想法。这可能是固定的， makemigrations 应该处理悬空引用，如果在迁移过程中较早删除引用的模型并稍后引用，则会发生悬空引用，因此您可以手动重新排列它们。