Django中唯一的BooleanField值？

Question

假设我的models.py是这样的:

class Character(models.Model):
    name = models.CharField(max_length=255)
    is_the_chosen_one = models.BooleanField()

我只想要我的一个Character实例is_the_chosen_one == True和其他所有实例is_the_chosen_one == False.如何才能最好地确保这种唯一性约束得到尊重？

考虑到尊重数据库,模型和(管理员)表单级别约束的重要性的答案的最高分!

Answer 1

每当我需要完成这个任务时,我所做的就是覆盖模型的save方法,并检查是否有其他模型已经设置了标志(并将其关闭).

class Character(models.Model):
    name = models.CharField(max_length=255)
    is_the_chosen_one = models.BooleanField()

    def save(self, *args, **kwargs):
        if self.is_the_chosen_one:
            try:
                temp = Character.objects.get(is_the_chosen_one=True)
                if self != temp:
                    temp.is_the_chosen_one = False
                    temp.save()
            except Character.DoesNotExist:
                pass
        super(Character, self).save(*args, **kwargs)

Answer 2

我会覆盖模型的save方法,如果你将boolean设置为True,请确保所有其他方法都设置为False.

from django.db import transaction

class Character(models.Model):
    name = models.CharField(max_length=255)
    is_the_chosen_one = models.BooleanField()

    def save(self, *args, **kwargs):
        if not self.is_the_chosen_one:
            return super(Character, self).save(*args, **kwargs)
        with transaction.atomic():
            Character.objects.filter(
                is_the_chosen_one=True).update(is_the_chosen_one=False)
            return super(Character, self).save(*args, **kwargs)

我尝试编辑Adam的类似答案,但因为改变了原来的答案而被拒绝了.这种方式更简洁,更有效,因为在单个查询中完成对其他条目的检查.

Answer 3

我没有使用自定义模型清理/保存,而是创建了一个覆盖方法的自定义字段.反而提高了一个错误,如果另一场是的,我所做的所有其他领域,如果它是.如果字段是并且没有其他字段,则不是引发错误,而是将字段保存为pre_savedjango.db.models.BooleanFieldTrueFalseTrueFalseTrueTrue

fields.py

from django.db.models import BooleanField


class UniqueBooleanField(BooleanField):
    def pre_save(self, model_instance, add):
        objects = model_instance.__class__.objects
        # If True then set all others as False
        if getattr(model_instance, self.attname):
            objects.update(**{self.attname: False})
        # If no true object exists that isnt saved model, save as True
        elif not objects.exclude(id=model_instance.id)\
                        .filter(**{self.attname: True}):
            return True
        return getattr(model_instance, self.attname)

# To use with South
from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^project\.apps\.fields\.UniqueBooleanField"])

models.py

from django.db import models

from project.apps.fields import UniqueBooleanField


class UniqueBooleanModel(models.Model):
    unique_boolean = UniqueBooleanField()

    def __unicode__(self):
        return str(self.unique_boolean)

Answer 4

在 Django 2.2 版之后，将这种约束添加到您的模型中会更简单。可以直接使用UniqueConstraint.condition。Django 文档

只需class Meta像这样覆盖您的模型：

class Meta:
    constraints = [
        UniqueConstraint(fields=['is_the_chosen_one'], condition=Q(is_the_chosen_one=True), name='unique_is_the_chosen_one')
    ]

Answer 5

以下解决方案有点难看但可能有效:

class MyModel(models.Model):
    is_the_chosen_one = models.NullBooleanField(default=None, unique=True)

    def save(self, *args, **kwargs):
        if self.is_the_chosen_one is False:
            self.is_the_chosen_one = None
        super(MyModel, self).save(*args, **kwargs)

如果将is_the_chosen_one设置为False或None,则它将始终为NULL.您可以根据需要使用NULL,但只能有一个True.

Answer 6

为了达到收支平衡,我发现其中一些问题成功解决了同一个问题,每个问题都适用于不同的情况:

我会选:

• @semente:尊重数据库,模型和管理表单级别的约束,同时尽可能地覆盖Django ORM.而且它可以大概一个内部使用 through的表ManyToManyField的unique_together情况.(我会检查并报告)

  class MyModel(models.Model):
      is_the_chosen_one = models.NullBooleanField(default=None, unique=True)
  
      def save(self, *args, **kwargs):
          if self.is_the_chosen_one is False:
              self.is_the_chosen_one = None
          super(MyModel, self).save(*args, **kwargs)
  

• @Flyte:仅在一个额外时间点击数据库并接受当前条目作为所选条目.干净优雅.

  from django.db import transaction
  
  class Character(models.Model):
      name = models.CharField(max_length=255)
      is_the_chosen_one = models.BooleanField()
  
  def save(self, *args, **kwargs):
      if not self.is_the_chosen_one:
          # The use of return is explained in the comments
          return super(Character, self).save(*args, **kwargs)  
      with transaction.atomic():
          Character.objects.filter(
              is_the_chosen_one=True).update(is_the_chosen_one=False)
          # The use of return is explained in the comments
          return super(Character, self).save(*args, **kwargs)  
  

其他解决方案不适合我的情况,但可行:

@nemocorp正在覆盖clean执行验证的方法.但是,它不报告哪个模型是"那个",这不是用户友好的.尽管如此,这是一个非常好的方法,特别是如果有人不打算像@Flyte那样具有攻击性.

@ saul.shanabrook和@Thierry J.会创建一个自定义字段,可以将任何其他"is_the_one"条目更改为False或者引发一个ValidationError.我只是不愿意为我的Django安装提供新功能,除非它是非常必要的.

@daigorocub:使用Django信号.我发现它是一种独特的方法,并提供了如何使用Django信号的提示.但是我不确定这是否严格地说 - "正确"使用信号,因为我不能将此过程视为"解耦应用程序"的一部分.

Answer 7

class Character(models.Model):
    name = models.CharField(max_length=255)
    is_the_chosen_one = models.BooleanField()

    def save(self, *args, **kwargs):
        if self.is_the_chosen_one:
            qs = Character.objects.filter(is_the_chosen_one=True)
            if self.pk:
                qs = qs.exclude(pk=self.pk)
            if qs.count() != 0:
                # choose ONE of the next two lines
                self.is_the_chosen_one = False # keep the existing "chosen one"
                #qs.update(is_the_chosen_one=False) # make this obj "the chosen one"
        super(Character, self).save(*args, **kwargs)

class CharacterForm(forms.ModelForm):
    class Meta:
        model = Character

    # if you want to use the new obj as the chosen one and remove others, then
    # be sure to use the second line in the model save() above and DO NOT USE
    # the following clean method
    def clean_is_the_chosen_one(self):
        chosen = self.cleaned_data.get('is_the_chosen_one')
        if chosen:
            qs = Character.objects.filter(is_the_chosen_one=True)
            if self.instance.pk:
                qs = qs.exclude(pk=self.instance.pk)
            if qs.count() != 0:
                raise forms.ValidationError("A Chosen One already exists! You will pay for your insolence!")
        return chosen

你也可以使用上面的表格来管理,只需使用

class CharacterAdmin(admin.ModelAdmin):
    form = CharacterForm
admin.site.register(Character, CharacterAdmin)

Answer 8

就这样。

def save(self, *args, **kwargs):
    if self.default_dp:
        DownloadPageOrder.objects.all().update(**{'default_dp': False})
    super(DownloadPageOrder, self).save(*args, **kwargs)

Answer 9

class Character(models.Model):
    name = models.CharField(max_length=255)
    is_the_chosen_one = models.BooleanField()

    def clean(self):
        from django.core.exceptions import ValidationError
        c = Character.objects.filter(is_the_chosen_one__exact=True)  
        if c and self.is_the_chosen:
            raise ValidationError("The chosen one is already here! Too late")

这样做可以在基本管理表单中进行验证