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📜  PositiveIntegerField – Django 模型

📅  最后修改于: 2022-05-13 01:55:08.022000             🧑  作者: Mango

PositiveIntegerField – Django 模型

PositiveIntegerField是Python中由int实例表示的整数。此字段类似于 IntegerField，但必须为正数或零 (0)。当 localize 为 False 或 TextInput 时，此字段的默认表单小部件是 NumberInput。它支持从 0 到 2147483647 的值在 Django 支持的所有数据库中都是安全的。它使用 MinValueValidator 和 MaxValueValidator 根据默认数据库支持的值来验证输入。

句法： 

field_name = models.PositiveIntegerField(**options)

Django 模型 PositiveIntegerField 解释

使用示例说明 PositiveIntegerField。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.PositiveIntegerField()

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.PositiveIntegerField()),
            ],
        ),
    ]

现在运行， 

Python manage.py migrate

因此，当您在项目上运行迁移时，会创建一个geeks_field PositiveIntegerField 。它是一个存储正整数的字段。

如何使用 PositiveIntegerField ？

PositiveIntegerField 用于存储在Python中由 int 实例表示的整数。要了解有关 int 的更多信息，请访问Python | int()函数。让我们尝试在 PositiveIntegerField 中保存一个正数。 

# importing the model
# from geeks app
from geeks.models import GeeksModel
  
# creating an instance of
# int
d = int(2189)
  
# creating a instance of 
# GeeksModel
geek_object = GeeksModel.objects.create(geeks_field = d)
geek_object.save()

现在让我们在管理服务器中检查它。我们已经创建了 GeeksModel 的一个实例。

PositiveIntegerField django 模型

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，将参数null = True添加到 PositiveIntegerField 将使其能够将该表的空值存储在关系数据库中。
以下是 PositiveIntegerField 可以使用的字段选项和属性。

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.