Django检查相关对象是否存在错误:RelatedObjectDoesNotExist

Question

has_related_object我的模型中有一个方法需要检查相关对象是否存在

class Business(base):
      name =  models.CharField(max_length=100, blank=True, null=True)

  def has_related_object(self):
        return (self.customers is not None) and (self.car is not None)


class Customer(base):
      name =  models.CharField(max_length=100, blank=True, null=True)
      person = models.OneToOneField('Business', related_name="customer")

但我得到错误:

Business.has_related_object()

RelatedObjectDoesNotExist:业务没有客户.

Answer 1

使用hasattr(self, 'customers')以避免异常支票在Django文档建议:

def has_related_object(self):
    return hasattr(self, 'customers') and self.car is not None

Answer 2

这是因为ORM必须转到数据库检查是否customer存在.由于它不存在,它引发了一个例外.

您必须将方法更改为以下内容:

def has_related_object(self):
    has_customer = False
    try:
        has_customer = (self.customers is not None)
    except Customer.DoesNotExist:
        pass
    return has_customer and (self.car is not None)

我不知道情况self.car所以我会留给你调整它,如果它需要它.

附注:如果您在具有ForeignKeyField或OneToOneField的模型上执行此操作,则可以执行以下操作以避免数据库查询.

def has_business(self):
    return self.business_id is not None

Answer 3

尽管这是一个老问题，但我认为这对于希望处理此类异常的人很有帮助，特别是当您想要检查 OneToOne 关系时。

我的解决方案是使用ObjectDoesNotExistfrom django.core.exceptions：

from django.core.exceptions import ObjectDoesNotExist

class Business(base):
      name =  models.CharField(max_length=100, blank=True, null=True)

    def has_related_object(self):
        try:
            self.customers
            self.car
            return True
        except ObjectDoesNotExist:
            return False


class Customer(base):
      name =  models.CharField(max_length=100, blank=True, null=True)
      person = models.OneToOneField('Business', related_name="customer")