如何强制 Django 模型中的 2 个字段共享相同的默认值? [英] How can I force 2 fields in a Django model to share the same default value?

问题描述

我有一个 Django 模型 MyModel，如下所示.

I have a Django model MyModel as shown below.

它有两个 DateTimeField 类型的字段:my_field1, my_field2

It has two fields of type DateTimeField: my_field1, my_field2

from django.db import models
from datetime import datetime

class MyModel(models.Model):
    my_field1 = models.DateTimeField(default=datetime.utcnow, editable=False)
    my_field2 = models.DateTimeField(
        # WHAT DO I PUT HERE?
    ) 

我希望两个字段都默认为 datetime.utcnow() 的值.但我想为两者保存相同的值.两次调用 utcnow() 似乎很浪费.

I want both fields to default to the value of datetime.utcnow(). But I want to save the same value for both. It seems wasteful to call utcnow() twice.

如何设置my_field2的默认值，使其简单地复制my_field1的默认值?

How can I set the default value of my_field2 so that it simply copies the default value of my_field1?

推荐答案

正确的方法是重写 save 方法而不是 __init__ 方法.实际上，不建议覆盖 init 方法，如果您希望控制对象的读取方式，则更好的方法是覆盖 from_db 或如果您想控制对象的保存方式，则覆盖 save 方法.

The proper way to do this is by over riding the save method rather than the __init__ method. In fact it's not recommended to over ride the init method, the better way is to over ride from_db if you wish to control how the objects are read or save method if you want to control how they are saved.

class MyModel(models.Model):
    my_field1 = models.DateTimeField(default=datetime.utcnow, editable=False)
    my_field2 = models.DateTimeField()

    def save(self, *arges, **kwargs):
        if self.my_field1 is None:
            self.my_field1 = datetime.utcnow()
            if self.my_field2 is None:
                self.my_field2 = self.my_field1

        super(MyModel, self).save(*args, **kwargs)

更新:我的声明参考:https://docs.djangoproject.com/en/1.9/ref/models/instances/

您可能会想通过覆盖 init 来自定义模型方法.但是，如果您这样做，请注意不要更改调用签名，因为任何更改都可能阻止模型实例保存.与其覆盖 init，不如尝试使用其中之一方法:

You may be tempted to customize the model by overriding the init method. If you do so, however, take care not to change the calling signature as any change may prevent the model instance from being saved. Rather than overriding init, try using one of these approaches:

这篇关于如何强制 Django 模型中的 2 个字段共享相同的默认值?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！