python - 在 Django 中创建另一个对象时创建对象

Question

当我在 Django 中创建另一个对象时是否可以创建对象？

我有这样的代码，我想首先创建 AnotherModel 实例，然后创建 Model 实例(在创建 AnotherModel 时)。

class Model(models.Model):
    name = models.CharFiled(max_length=50)

class AnotherModel(models.Model):
    model = models.ForeignKey(Model, on_delete=models.CASCADE)
    description = models.TextField()

我尝试使用 Django 信号 - pre_save。

@receiver(pre_save, sender=AnotherModel)
def save_model(sender, **kwargs):
    # some code

但我有这样的异常(exception):

ValueError:无法分配“u'Test”:“AnotherModel.resource”必须是“Model”实例。

Answer 1

Is it possible to create object when I created another object in Django?

是的，可以，你有两个选择吗:

1) 选项 1:覆盖保存 ( Overriding predefined model methods )

from django.db import models

class AnotherModel(models.Model):
    model = models.ForeignKey(Model, on_delete=models.CASCADE)
    description = models.TextField()

    def save(self, *args, **kwargs):
        if self.pk is None:  # create
            self.model = Model.objects.create( name = "some random name" )
        super().save(*args, **kwargs)  # Call the "real" save() method.

2) 选项 2:Using pre-save signal :

from django.db.models.signals import pre_save
from django.dispatch import receiver    

@receiver(pre_save, sender=AnotherModel)
def my_handler(sender, **kwargs):
    if sender.pk is None:  # create
        sender.model = Model.objects.create( name = "some random name" )

重要:

必须先创建相关模型才能保存当前模型。在我使用的示例中:

Model.objects.create( name = "some random name" )

但是您可以按照常规方式创建模型:

m = Model()
m.name = "random name"
m.save()  # <--- important!