如何检查外键是否存在？

Question

在这里，我有一个模型Staff，它与 djangoUser模型有 OneToOne 关系，与模型有外键关系。在Organization这里删除组织时，我想检查组织是否存在于 Staff 模型中。如果它存在于 Staff 模型中，那么我不想删除但如果它不存在于其他表中，那么只有我想删除。

我该怎么做 ？

我使用以下代码收到此错误：

Exception Type: TypeError
Exception Value:    
argument of type 'bool' is not iterable

模型.py

class Organization(models.Model):
    name = models.CharField(max_length=255, unique=True)
    slug = AutoSlugField(unique_with='id', populate_from='name')
    logo = models.FileField(upload_to='logo', blank=True, null=True)

class Staff(models.Model):
    user = models.OneToOneField(get_user_model(), on_delete=models.CASCADE, related_name='staff')
    name = models.CharField(max_length=255, blank=True, null=True)
    organization = models.ForeignKey(Organization, on_delete=models.SET_NULL, blank=True, null=True,
                                     related_name='staff')

视图.py

def delete_organization(request, pk):
    organization = get_object_or_404(Organization, pk=pk)
    if organization in organization.staff.all().exists():
        messages.error(request,"Sorry can't be deleted.")
        return redirect('organization:view_organizations')
# also tried
# if organization in get_user_model().objects.filter(staff__organization=organizatin).exists():
    elif request.method == 'POST' and 'delete_single' in request.POST:
        organization.delete()
        messages.success(request, '{} deleted.'.format(organization.name))
        return redirect('organization:view_organizations')

Answer 1

支票应该是：

def delete_organization(request, pk):
    organization = get_object_or_404(Organization, pk=pk)
    if organization.staff.exists():
        messages.error(request, "Sorry can't be deleted.")
        return redirect('organization:view_organizations')
    # ...

但是，您可以通过在以下内容中进行适当的过滤来优化上述内容get_object_or_404：

def delete_organization(request, pk):
    organization = get_object_or_404(Organization, pk=pk, is_staff__isnull=True)
    # ...

如果组织不存在，或者组织存在但仍有一些员工，这将引发 404。

根据您编写的逻辑，您要防止在仍有员工的情况下删除组织。您也可以使用作为处理程序在模型层中设置此类逻辑：models.PROTECTon_delete

class Staff(models.Model):
    user = models.OneToOneField(get_user_model(), on_delete=models.CASCADE, related_name='staff')
    name = models.CharField(max_length=255, blank=True, null=True)
    organization = models.ForeignKey(Organization, on_delete=models.PROTECT, blank=True, related_name='staff')

现在 Django 将帮助您确保您不会意外删除Organization仍然有相关人员的地方，这使其更安全。