我如何修理我的Django“；ValueError：发现错误数量的约束“0”；迁移错误？

我正在使用Python3.7和Django。我尝试了这个解决方案，但仍然得到了同样的错误。我的一次迁移遇到了问题。我最近更新了我的模型的唯一约束

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')},
        ),
      ]

但当我运行迁移时，我遇到了一个令人困惑的错误，抱怨“ValueError:找到了错误数量（0）的约束”

（venv）localhost:articlesum\u项目davea$python manage.py迁移articlesum
要执行的操作：
应用所有迁移：articlesum
运行迁移：
正在应用articlesum.0033_auto_20190830_1128…回溯（最近一次调用）：
文件“manage.py”，第21行，在
从命令行（sys.argv）执行命令
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/___init__.py”，第381行，从命令行执行
utility.execute（）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/______.py”，执行中第375行
self.fetch_命令（子命令）。从_argv（self.argv）运行_
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/base.py”，第316行，从_argv运行
self.execute（*args，**cmd_选项）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/base.py”，第353行，在execute中
输出=self.handle（*args，**选项）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/base.py”，第83行，包装
res=句柄函数（*args，**kwargs）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/core/management/commands/migrate.py”，第203行，在handle中
假首字母=假首字母，
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/migrations/executor.py”，第117行，在migrate中
状态=self.\u迁移\u所有\u转发（状态，计划，完整计划，假=假，假首字母=假首字母）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/migrations/executor.py”，第147行，全部向前迁移
state=self.apply\u迁移（state，migration，false=false，false\u initial=false\u initial）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/migrations/executor.py”，第244行，在apply_migration中
state=migration.apply（状态，模式编辑器）
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/migrations/migration.py”，第124行，在apply中
操作。数据库转发（self.app\u标签、模式编辑器、旧状态、项目状态）
数据库中的文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/migrations/operations/models.py”，第514行
getattr（新的\模型。\元，self.option \名称，set（）），
文件“/Users/davea/Documents/workspace/articlesum_project/venv/lib/python3.7/site packages/django/db/backends/base/schema.py”，第356行，在alter_unique_中
self.\u delete\u组合索引（模型，字段，{'unique'：True}，self.sql\u delete\u unique）
文件“/Users/davea/Documents/workspace/articlesum\u project/venv/lib/python3.7/site packages/django/db/backends/base/schema.py”，第385行，在删除索引中
“，”。连接（列），
ValueError:为articlesum\u articlesumstatbyhour（网站id、已用时间（以秒为单位）、小时（以天为单位）找到了错误数量（0）的约束

---

为什么迁移无法创建我的唯一约束？

当前迁移似乎正在查找数据库当前没有的上一个索引。因此，您需要在db表上设置最后一个唯一索引

每次更改表上的索引时，它都会检查其以前的索引并删除它。在您的情况下，它无法获取上一个索引

---

解决方案-1.您可以手动生成它2.或者还原到使用以前索引的代码并进行迁移。然后最后在代码中更改为新索引并运行迁移。（需要处理django_迁移文件）

迁移中缺少一组括号，可能是因为您使用的是元组。请尝试

unique\u-together=[[“一天中的一小时”，“网站”]

或

unique\u-together=[“一天中的一小时”，“网站”]

感谢您的建议，但遗憾的是，这两种方法都不起作用（都产生了相同的错误）在添加此约束之前，您有其他约束吗？不确定--我从离开项目的其他人那里继承了此代码库。有没有办法检查这类事情？是的，翻阅以前的迁移文件。我认为有一个悬而未决的问题，Django没有正确地删除约束。因此，您可能应该自己创建一个迁移文件，在该文件添加新约束之前删除先前的约束。

(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)