django - 如果我们从 html 输入新的输入,UUID 会重复吗?
问题描述
出现错误 - 我将一个表单从 html 保存到我的数据库中,而当我尝试保存下一个表单时,它给了我这个错误 - 客户处的 IntegrityError (1062, "Duplicate entry 'ad138e46-edc0-11va-b065-a41g7252ecb4'' for key 'customer .PRIMARY'") 请在 models.py 中解释我的 uuid 是 -
class customer(models.Model):
customerid = models.CharField(default=str(uuid.uuid4()), max_length=500, primary_key=True)
customername=models.CharField(max_length=100)
好心的帮助
更新
表格.py
class createcustomerform(ModelForm):
class Meta:
model=customer
fields=[
'customername']
更新了 Models.py
import uuid
from uuid import UUID
from django.contrib.auth.models import User
from django.dispatch.dispatcher import receiver
from django.utils.translation import ugettext_lazy as _
from django.db.models.signals import pre_save
class customer(UUIDMixin,models.Model):
customername=models.CharField(max_length=100)
def __str__(self):
return self.customername
class UUIDMixin(models.Model):
uuid = models.UUIDField(blank=True,db_index=True,default=None,help_text=_('Unique identifier'),max_length=255,null=True,unique=True,verbose_name=_('UUID'))
class Meta:
abstract = True
@classmethod
def check_uuid_exists(cls, _uuid):
#Determine whether UUID exists """
manager = getattr(cls, '_default_manager')
return manager.filter(uuid=_uuid).exists()
@classmethod
def get_available_uuid(cls):
#Return an Available UUID """
row_uuid = uuid.uuid4()
while cls.check_uuid_exists(uuid=row_uuid):
row_uuid = uuid.uuid4()
return row_uuid
@receiver(pre_save)
def uuid_mixin_pre_save(sender, instance, **kwargs):
if issubclass(sender, UUIDMixin):
if not instance.uuid:
manager = getattr(instance.__class__, '_default_manager')
use_uuid = uuid.uuid4()
while manager.filter(uuid=use_uuid):
use_uuid = uuid.uuid4()
instance.uuid = use_uuid
#Automatically populate the uuid field of UUIDMixin models if not already populated.
解决方案
您应该使用适当的UUIDField
并避免设置默认值。
确保在创建对象时设置该值,并确保该值是唯一的 - 显然 UUID 中重复的机会非常小,这就是重点。
您可以自己创建一个模型 mixin,它将 a 添加uuid
到您的模型中,并确保在保存对象时设置该值;
class UUIDMixin(models.Model):
"""
Mixin for models contain a unique UUID, gets auto-populated on save
"""
uuid = models.UUIDField(
blank=True,
db_index=True,
# default=uuid.uuid4,
# NB: default is set to None in migration to avoid duplications
default=None,
help_text=_('Unique identifier'),
max_length=255,
null=True,
unique=True,
verbose_name=_('UUID'),
)
class Meta:
"""Metadata for the UUIDMixin class"""
abstract = True
@classmethod
def check_uuid_exists(cls, _uuid):
""" Determine whether UUID exists """
manager = getattr(cls, '_default_manager')
return manager.filter(uuid=_uuid).exists()
@classmethod
def get_available_uuid(cls):
""" Return an Available UUID """
row_uuid = uuid.uuid4()
while cls.check_uuid_exists(uuid=row_uuid):
row_uuid = uuid.uuid4()
return row_uuid
@receiver(pre_save)
def uuid_mixin_pre_save(sender, instance, **kwargs):
"""
Automatically populate the uuid field of UUIDMixin models if not already
populated.
"""
if issubclass(sender, UUIDMixin):
if not instance.uuid:
manager = getattr(instance.__class__, '_default_manager')
use_uuid = uuid.uuid4()
while manager.filter(uuid=use_uuid):
use_uuid = uuid.uuid4()
instance.uuid = use_uuid
根据您的评论,让我解释更多。
上面是一个抽象模型,这意味着它本身不会创建表,它可以被其他(具体)模型使用,以便他们可以使用它定义的内容。
这是类和继承的好处。允许您不要在对许多模型有用的东西上重复代码。
不,在元数据中你会看到abstract = True
。所以你定义你的模型,它会从这个抽象模型中MyModel(UUIDMixin, models.Model)
获取一个字段以及你定义的任何内容。uuid
你会通过做这样的事情来使用它;
class Customer(UUIDMixin, models.Model):
name = models.CharField(max_length=100)
如果你真的想使用 UUID 作为主键,可以设置两个 mixin, aPrimaryUUIDMixin
和 the UUIDMixin
,因为总的来说,主键上较小的值可能更有效。
你还提到Undefined variable: _
通常在 django 中,您会在文件顶部看到这样的导入;
from django.utils.translation import ugettext_lazy as _
然后将其用于包装字符串以便可以翻译它们,例如,_("Hello")
即使您不翻译您的项目,也通常只包含此内容。你可以在这里阅读;https://docs.djangoproject.com/en/3.1/topics/i18n/translation/#standard-translation