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📜  UUIDField – Django 模型

📅  最后修改于: 2022-05-13 01:54:28.556000             🧑  作者: Mango

UUIDField – Django 模型

UUIDField 是一个存储通用唯一标识符的特殊字段。它使用 Python 的 UUID 类。 UUID，Universal Unique Identifier，是一个Python库，有助于生成 128 位的随机对象作为 id。它提供了唯一性，因为它根据时间、计算机硬件（MAC 等）生成 ID。通用唯一标识符是primary_key的 AutoField 的一个很好的替代方案。数据库不会为你生成 UUID，所以建议使用default 。

例如， 

import uuid
from django.db import models
  
class MyUUIDModel(models.Model):
    id = models.UUIDField(
         primary_key = True,
         default = uuid.uuid4,
         editable = False)
    # other fields

句法

field_name = models.UUIDField(**options)

Django Model UUID字段说明

使用示例说明 UUIDField。考虑一个名为geeks的项目，它有一个名为geeksforgeeks的应用程序。

在极客应用的models.py文件中输入以下代码。 

from django.db import models
from django.db.models import Model
# Create your models here.
  
class GeeksModel(Model):
    geeks_field = models.UUIDField()

将极客应用添加到INSTALLED_APPS 

# Application definition
  
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'geeks',
]

现在，当我们从终端运行makemigrations命令时， 

Python manage.py makemigrations

将在geeks目录中创建一个名为 migrations 的新文件夹，其中包含一个名为0001_initial.py的文件

# Generated by Django 2.2.5 on 2019-09-25 06:00
  
from django.db import migrations, models
  
class Migration(migrations.Migration):
  
    initial = True
  
    dependencies = [
    ]
  
    operations = [
        migrations.CreateModel(
            name ='GeeksModel',
            fields =[
                ('id', 
                  models.AutoField(auto_created = True,
                  primary_key = True,
                  serialize = False, 
                  verbose_name ='ID'
                )),
                ('geeks_field', 
                  models.UUIDField()
                 )),
            ],
        ),
    ]

因此，在项目上运行 makemigrations 时会创建一个geeks_field UUIDField 。它是一个存储 python 的 UUID 实例的字段。

如何使用 UUIDField ？

UUID，Universal Unique Identifier，是一个Python库，有助于生成 128 位的随机对象作为 id。要了解有关 UUID 的更多信息，请访问在Python中使用 UUID 生成随机 id。让我们尝试将一个 uuid 对象保存到 UUIDField 中。 

# importing the model
# from geeks app
from geeks.models import GeeksModel
  
# importing uuid
import uuid
  
# creating an instance of
# uuid object
test = uuid.uuid4()
  
# creating a instance of 
# GeeksModel
geek_object = GeeksModel.objects.create(geeks_field = test)
geek_object.save()

现在让我们在管理服务器中检查它。我们创建了一个 GeeksModel 实例
UUIDField-django-models

字段选项

字段选项是赋予每个字段的参数，用于应用某些约束或将特定特征赋予特定字段。例如，向 UUIDField 添加参数null = True将使其能够在关系数据库中存储该表的空值。
以下是 UUIDField 可以使用的选项和属性。

Field OptionsDescription
NullIf True, Django will store empty values as NULL in the database. Default is False.
BlankIf True, the field is allowed to be blank. Default is False.
db_columnThe name of the database column to use for this field. If this isn’t given, Django will use the field’s name.
DefaultThe default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.
help_textExtra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.
primary_keyIf True, this field is the primary key for the model.
editableIf False, the field will not be displayed in the admin or any other ModelForm. They are also skipped during model validation. Default is True.
error_messagesThe error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override.
help_textExtra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.
verbose_nameA human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces.
validatorsA list of validators to run for this field. See the validators documentation for more information.
UniqueIf True, this field must be unique throughout the table.