英文:
Django constraint for "field one not in field two for any row"?
问题
假设我有一个Django模型，其中包含两个字段one和two：
class MyModel(models.Model):
one = models.CharField(max_length=100, unique=True)
two = models.CharField(max_length=100)
unique=True 表示如果我尝试插入一个具有one="one"的行，而另一个具有相同值的行已经存在，将违反唯一约束。
我应该如何创建一个Django约束，以确保如果存在一个one="one"的行，就不能插入一个two="one"的行？
英文:
Suppose I have a Django model with two fields one and two:
class MyModel(models.Model):
one = models.CharField(max_length=100, unique=True)
two = models.CharField(max_length=100)
unique=True means if I try to put in a row with one="one" when another such row already exists, a unique constraint will be violated.
How would I make a Django constraint that says if there is a row with one="one", then I can't put in a row with two="one"?
This does seem related to this question and this answer, but I don't quite see the answer to my question.
答案1
得分: 1
models.py
从Hemal Petal提到的，对于这种自定义验证，我发现最好的方法是重写保存方法：
from django.core.exceptions import ValidationError
def save(self, *args, **kwargs):
if MyModel.objects.filter(
two=self.one
).exists():
raise ValidationError(f'{self.one} already exists in column two!')
return super().save(*args, **kwargs)
英文:
For custom validation like this I've found it best to override the save method, as @Hemal Petal mentioned:
models.py
from django.core.exceptions import ValidationError
def save(self, *args, **kwargs):
if MyModel.objects.filter(
two=self.one
).exists():
raise ValidationError(f'{self.one} already exists in column two!')
return super().save(*args, **kwargs)
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