python - 添加 Django 模型约束？

Question

我的模型 Period 如下:

class Period(models.Model):
      number = models.PositiveIntegerField(primary_key=True)
      start_time = models.TimeField()
      end_time = models.TimeField()

我如何添加约束来制作Period.start_time < Period.end_time和 Period 模型有这样的顺序吗？

Period 1: 7:00-7:50; Period 2: 7:50-8:40; ...

字段编号表示周期实例的顺序。我的方法是添加方法来检查它是否有效。但是，我想知道有什么数据库方法可以做到这一点。

Answer 1

你可以通过多种方式做到这一点

方法-1:重写Period模型的save()方法为

<b>from django.core.exceptions import ValidationError</b>


class Period(models.Model):
    number = models.PositiveIntegerField(primary_key=True)
    start_time = models.TimeField()
    end_time = models.TimeField()

    <b>def save(self, *args, **kwargs):
        if self.end_time < self.start_time:
            raise ValidationError("some message")
        super().save(*args, **kwargs)</b>

方法-2:重写模型的clean()方法

<b>from django.core.exceptions import ValidationError</b>


class Period(models.Model):
    number = models.PositiveIntegerField(primary_key=True)
    start_time = models.TimeField()
    end_time = models.TimeField()

    <b>def clean(self):
        super().clean()  # calling default cleaning
        if self.end_time < self.start_time:
            raise ValidationError("some message")</b>

方法- 3:覆盖full_clean()方法

<b>from django.core.exceptions import ValidationError</b>


class Period(models.Model):
    number = models.PositiveIntegerField(primary_key=True)
    start_time = models.TimeField()
    end_time = models.TimeField()

    <b>def full_clean(self, exclude=None, validate_unique=True):
        super().full_clean(exclude=None, validate_unique=True)  # calling default full_clean
        if self.end_time < self.start_time:
            raise ValidationError("some message")</b>

引用
1. Model.clean() - Django doc
2. Model.save() - Django doc
3. Model.full_clean() - Django doc