python - Django 信号中 Unresolved 错误

Question

我想在保存实例 Musician 模型时使用 pre_save 函数填充 Album 模型的 artist 字段。

模型.py

class Musician(models.Model):
    first_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)
    instrument = models.CharField(max_length=100)

    def __str__(self):
        return self.first_name



class Album(models.Model):
    artist = models.ForeignKey(Musician, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)
    release_date = models.DateField(null=True,blank=True)
    num_stars = models.IntegerField(null=True,blank=True)

    def __str__(self):
        return self.artist

@receiver(pre_save,sender = Musician)
def create_album(sender,instance,**kwargs):
    sm = Album()
    sm.artist = instance
    sm.save()

但是当我尝试从管理员创建音乐家模型的实例时，它会在点击保存按钮时显示此错误。

Exception Type: ValueError at /admin/sig/musician/add/
Exception Value: save() prohibited to prevent data loss due to unsaved related object 'artist'.

我不明白如何解决这个 sm.save() 错误!请帮助我。

Answer 1

pre_save 信号正在调用 before Musician 实例保存到数据库。但是您不能将未保存的实例设置为艺术家值。您应该将信号更改为 post_save。在这种情况下，音乐家将在专辑创建时被保存:

@receiver(post_save,sender = Musician)
def create_album(sender,instance,**kwargs):
    sm = Album()
    sm.artist = instance
    sm.save()