python - Django: AttributeError: 'UniqueConstraint' 对象没有属性 'fields_orders'

Question

我的应用程序中有一个名为“就业”的模型，它引用了两个名为“用户”和“公司”的模型。在数据库的 Employments 表中，两个外键上有一个复合索引，防止同一用户在同一家公司有两个职位。我正在尝试使用 UniqueConstraint 类在 Django 中表示此复合索引，但它抛出了一个错误，我找不到任何文档。

这个模型通常工作得很好。但是，当我将 UniqueConstraint 添加到模型的索引时，服务器会抛出错误。我查看了 UniqueConstraint 的文档，以及 Django 文档的其余部分，但找不到任何关于我收到的错误的提及。我还尝试在 UniqueConstraint 的字段参数中将“User_ID”和“Company_ID”替换为“user”和“company”，但我得到了完全相同的错误。

不确定这是否与问题相关，但我在 python:3.6 容器和 Django 版本 2.2 中运行带有 Docker 的 Django 服务器。

这是 Employment 模型:

from django.db import models
from app.models import User, Company

class Employment(models.Model):
    Employment_ID = models.AutoField(primary_key=True)
    user          = models.ForeignKey(User, db_column='User_ID', on_delete=models.CASCADE)
    company       = models.ForeignKey(Company, db_column='Company_ID', on_delete=models.CASCADE)

    class Meta:
        db_table = "Employments"
        indexes = [
            models.UniqueConstraint(fields=['User_ID', 'Company_ID'],
                                    name='Employment_User_Company_UNIQUE') # server works fine without this
        ]

当我启动我的 Django 服务器时，我得到以下输出:

Watching for file changes with StatReloader
Performing system checks...

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/utils/autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/commands/runserver.py", line 117, in inner_run
    self.check(display_num_errors=True)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py", line 390, in check
    include_deployment_checks=include_deployment_checks,
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py", line 377, in _run_checks
    return checks.run_checks(**kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/core/checks/registry.py", line 72, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/usr/local/lib/python3.6/site-packages/django/core/checks/model_checks.py", line 31, in check_all_models
    errors.extend(model.check(**kwargs))
  File "/usr/local/lib/python3.6/site-packages/django/db/models/base.py", line 1254, in check
    *cls._check_indexes(),
  File "/usr/local/lib/python3.6/site-packages/django/db/models/base.py", line 1565, in _check_indexes
    fields = [field for index in cls._meta.indexes for field, _ in index.fields_orders]
  File "/usr/local/lib/python3.6/site-packages/django/db/models/base.py", line 1565, in <listcomp>
    fields = [field for index in cls._meta.indexes for field, _ in index.fields_orders]
AttributeError: 'UniqueConstraint' object has no attribute 'fields_orders'

如果有人遇到过此错误或知道解决方法，我将非常感谢您的见解。

Answer 1

您在 indexes 参数中定义了它，但这应该在 constraints [Django-doc] 中属性。顾名思义，indexes 包含在表上定义的索引列表。另一方面，constraints 包含应该强制执行的约束。

class Employment(models.Model):
    Employment_ID = models.AutoField(primary_key=True)
    user = models.ForeignKey(User, db_column='User_ID', on_delete=models.CASCADE)
    company = models.ForeignKey(Company, db_column='Company_ID', on_delete=models.CASCADE)

    class Meta:
        db_table = "Employments"
        <b>constraints</b> = [
            models.UniqueConstraint(
                fields=['User_ID', 'Company_ID'],
                name='Employment_User_Company_UNIQUE'
            )
        ]