在DJANGO模型中添加条件外键字段

Question

Models.py如下所示。 Release表有一个指向SystemRequirement表的外键system_requirements_id ，但我希望只有当 Release表中的system_requirements字段中没有文本时 ，用户才应填写system_requirements_id 。 否则， system_requirements_id可以留空。 我该如何实现？

class SystemRequirement(TimeStampedModel):
    code_name = models.TextField(blank=True)
    content = models.TextField()
    creation_date = models.DateField(auto_now=False, auto_now_add=True)

    def __unicode__(self):
        return self.code_name

class Release(TimeStampedModel):
    system_requirements = models.TextField(blank=True)
    system_requirements_id = models.ForeignKey(SystemRequirement,
    blank=True, null=True)

Answer 1

我的建议是： -

Models.py -

class Release(TimeStampedModel):
    system_requirements_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    system_requirements = models.TextField(blank=True)



class SystemRequirement(TimeStampedModel):
    system_requirements_id = models.ForeignKey(Release)
    code_name = models.TextField(blank=True)
    content = models.TextField()
    creation_date = models.DateField(auto_now=False, auto_now_add=True)

    def __unicode__(self):
        return self.code_name

views.py-（查询）

#check system_requirements text in Release table
try:
    SystemRequirement =     Release.objects.get(system_requirements='MatchingText')

    #If got matching result means text exist so don't do anything

except ObjectDoesNotExist: #No matching query
    Release.objects.filter(system_requirements='MatchingText').update(system_requirements_id='SomeId')