Question

当我尝试运行Django migrate命令时，我收到“关系列已存在”错误：

Operations to perform:
  Synchronize unmigrated apps: signin, django_rq, gis, staticfiles, admindocs, messages, pipeline, test_without_migrations, django_extensions
  Apply all migrations: profile, activities, contenttypes, # plus other modules...
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying activities.0002_auto_20170731_1939...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/core/management/base.py", line 393, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/core/management/base.py", line 444, in execute
    output = self.handle(*args, **options)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/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 "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/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 "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 148, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/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 "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 62, in database_forwards
    field,
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/contrib/gis/db/backends/postgis/schema.py", line 94, in add_field
    super(PostGISSchemaEditor, self).add_field(model, field)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 398, in add_field
    self.execute(sql, params)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 111, in execute
    cursor.execute(sql, params)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/utils.py", line 97, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/srv/http/example.com/venvs/4dc40e5fc12700640a30ae0f040aa07ffc8aa1c5/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: column "country_id" of relation "travel" already exists

Travel类继承自Activities类：

# activities/models.py
from profile.models import Country

class Activity(models.Model):
    host = models.ForeignKey(User)
    # other fields...

    class Meta:
        abstract = True

class Travel(Activity):
    start_date = models.DateField()
    country = models.ForeignKey(Country)
    # other fields...

外键引用的国家/地区类位于另一个模块中。它本质上是一个包含代码（缩写）和的代码表每个国家/地区的名称：

# profile/models.py
class Country(models.Model):
    country_cd = models.CharField(max_length=2)
    descrip = models.CharField(max_length=50)

除了活动有两个迁移文件（我不太明白）之外，我在迁移文件中看不到任何异常：

# activities/migrations/0001_initial.py
class Migration(migrations.Migration):

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Travel',
            fields=[
                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
                ('name', models.CharField(max_length=256)),
                # other fields but none that reference Country
            ],
            options={
                'db_table': 'travel',
            },
        ),
    ]

# activities/migrations/0002_auto_20170731_1939.py
class Migration(migrations.Migration):

    dependencies = [
        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
        ('profile', '0001_initial'),
        ('activities', '0001_initial'),
    ]

    operations = [
        migrations.AddField(
            model_name='travel',
            name='country',
            field=models.ForeignKey(to='profile.Country'),
        ),
        migrations.AddField(
            model_name='travel',
            name='host',
            field=models.ForeignKey(to=settings.AUTH_USER_MODEL),
        ),
        # other fields...
    ]

我不明白为什么我收到这个错误。我注意到我在其他声明外键关系的模型中没有这个问题。但是，在所有这些模型中，外键关系是auth.models.User或同一模型文件中的另一个类。我最近阅读了一篇文章Tips for Building High-Quality Django Apps at Scale，其中作者说如果你有跨应用程序外键，你可能会遇到运行迁移的问题，所以问题可能与此有关。我可以在活动模块中重新创建“Country”类，但这不会是DRY。我不知道如何解决这个问题。

Answer 1

如果数据库中已存在travel.country字段，则无法运行迁移。您可以使用--fake选项将迁移标记为已应用，而无需实际运行SQL。

./manage.py migrate activities 0002_auto_20170731_1939 --fake

Answer 2

正如Alasdair所说，你无法覆盖现有的列。当我做这样的事情时 - 必须删除表并重新创建具有明确迁移的新表。

Answer 3

对于抽象类中的ForeignKey或ManyToManyField，添加如下相关名称： related_name = “％（app_label）■_％（类）s_related”，

如果您还使用related_query_name，请添加以下内容： related_query_name = “％（app_label）■_％（类）SS”，

修复'列已存在'Django迁移错误？

3 个答案: