DurationField – Django 模型

DurationField 是一个用于存储时间段的字段——在Python中由 timedelta 建模。在 PostgreSQL 上使用时，使用的数据类型是间隔，而在 Oracle 上，数据类型是 INTERVAL DAY(9) TO SECOND(6)。否则，将使用微秒的 bigint。 DurationField 基本上存储一个持续时间，即两个日期或时间之间的差异。

句法

field_name = models.DurationField(**options)

Django 模型持续时间字段说明

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

Refer to the following articles to check how to create a project and an app in Django. 

• How to Create a Basic Project using MVT in Django?
• How to Create an App in Django ?

在极客应用的models.py文件中输入以下代码。

Python3

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

将极客应用添加到 INSTALLED_APPS

Python3

# 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

Python3

# 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.DurationField()),
            ],
        ),
    ]

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 DurationField 。它是一个存储 datetime.timedelta Python对象的字段。

如何使用 DurationField ？

DurationField 用于在数据库中存储Python datetime.timedelta 实例。可以根据数据库中的时间或日期存储任何类型的持续时间。要了解有关 datetime.timedelta 的更多信息，请查看Python | datetime.timedelta()函数。让我们尝试在上面创建的模型中存储一个 timedelta 实例。

Python3

# importing the model
# from geeks app
from geeks.models import GeeksModel
 
# importing datetime module
import datetime
 
# creating an instance of
# datetime.timedelta
d = datetime.timedelta(days =-1, seconds = 68400)
 
# creating an 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。

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 DurationField 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 DurationField 可以使用的字段选项和属性。

Field Options	Description
Null	If True, Django will store empty values as NULL in the database. Default is False.
Blank	If True, the field is allowed to be blank. Default is False.
db_column	The name of the database column to use for this field. If this isn’t given, Django will use the field’s name.
Default	The 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_text	Extra “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_key	If True, this field is the primary key for the model.
editable	If 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_messages	The 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_text	Extra “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_name	A 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.
validators	A list of validators to run for this field. See the validators documentation for more information.
Unique	If True, this field must be unique throughout the table.