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django - 如何修复我的 Django“ValueError: Found wrong number (0) of constraints”迁移错误？

问题描述

我正在使用 Python 3.7 和 Django。我尝试了这个解决方案——在 Django 迁移期间收到“ValueError: Found wrong number (0) of constraints for ...”，但仍然出现同样的错误。我的一项迁移遇到了麻烦。我最近更新了我的模型的独特约束......

class ArticleSumStatByHour(models.Model):
    total_score = models.DecimalField(default=0, max_digits=12, decimal_places=2, null=False)
    total_seconds_to_reach_fp = models.DecimalField(default=0, max_digits=12, decimal_places=2, null=False)
    num_articles = models.IntegerField(default=0, null=False)
    hour_of_day = IntegerField(
        null=False,
        validators=[
            MaxValueValidator(23),
            MinValueValidator(0)
        ]
    )
    index = models.FloatField(default=0)
    website = models.ForeignKey(website, on_delete=models.CASCADE, related_name='articlesumstatbyhoursub')

        class Meta:
            unique_together = ("hour_of_day","website")

这是我的迁移，

...
class Migration(migrations.Migration):

    dependencies = [
        ('articlesum', '0032_auto_20190808_1452'),
    ]

    operations = [
        migrations.AlterField(
            model_name='articlesumstatbyhour',
            name='website',
            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='articlesumstatbyhoursub', to='articlesum.website'),
        ),
        migrations.AlterUniqueTogether(
            name='articlesumstatbyhour',
            unique_together={('hour_of_day','website')},
        ),
      ]

但是当我运行迁移时，我收到了这个令人费解的错误，抱怨“ValueError：发现错误数量（0）的约束”......

(venv) localhost:articlesum_project davea$ python manage.py migrate articlesum
Operations to perform:
  Apply all migrations: articlesum
Running migrations:
  Applying articlesum.0033_auto_20190830_1128...Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/core/management/commands/migrate.py", line 203, in handle
    fake_initial=fake_initial,
  File "/Users/davea/Documents/workspace/articlesum_project/venv/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 "/Users/davea/Documents/workspace/articlesum_project/venv/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 "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/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 "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/db/migrations/operations/models.py", line 514, in database_forwards
    getattr(new_model._meta, self.option_name, set()),
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/db/backends/base/schema.py", line 356, in alter_unique_together
    self._delete_composed_index(model, fields, {'unique': True}, self.sql_delete_unique)
  File "/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site-packages/django/db/backends/base/schema.py", line 385, in _delete_composed_index
    ", ".join(columns),
ValueError: Found wrong number (0) of constraints for articlesum_articlesumstatbyhour(website_id, elapsed_time_in_seconds, hour_of_day)

为什么迁移无法创建我的唯一约束？

标签： djangopython-3.xmigrationunique-constraint

解决方案

当前的迁移似乎正在寻找您的数据库当前没有的先前索引。因此，您将需要设置了最后一个唯一索引的 db 表。

每次更改表上的索引时，它都会检查其先前的索引并将其删除。在您的情况下，它无法获取先前的索引。

解决方案- 1.您可以手动生成它 2.或者恢复到使用以前索引的代码并迁移。最后在代码中更改为新索引并运行迁移。（要处理的 django_migration 文件）

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