如果字段存在，Django过滤查询集答案

【问题标题】：Django filter queryset if a field exists如果字段存在，Django过滤查询集
【发布时间】：2015-05-06 16:43:30
【问题描述】：

当且仅当loan 存在于我的模型ShgGroupLoanMarking 中时，我想过滤我的查询集。

class ShgGroupLoanMarking(models.Model):
 shg = models.ForeignKey(Shg, null=True)
 category = models.CharField(max_length=25, choices=GROUP_CATEGORY, default="shg_group")
 msss = models.ForeignKey(Msss, null=True)
 shgmember = models.ForeignKey(ShgMember, null=True)
 loan = models.ForeignKey(Loan, null=True)
 date_of_marking = models.DateField(null=True)
 paid = models.CharField(max_length=100, null=True)
 loan_amount = models.CharField(max_length=100, null=True)
 service_charge = models.CharField(max_length=100, null=True)
 description = models.CharField(max_length=100, null=True)
 status = models.CharField(max_length=100, null=True)
 print_status = models.BooleanField(default=False)
 sent_to_bank_status = models.BooleanField(default=False)
 receipt_number = models.IntegerField(default=0)

如何做到这一点？

【问题讨论】：

标签： django django-queryset django-filter

【解决方案1】：

ShgGroupLoanMarking.objects.filter(loan__isnull=False)

或

ShgGroupLoanMarking.objects.exclude(loan=None)

【讨论】：

这实际上并不测试一个字段是否存在，它假定它存在并检查它是否为空。如果该字段确实不存在，这仍然会抛出 jango.core.exceptions.FieldError: Cannot resolve keyword '....' into field.