python之Django 信号中 Unresolved 错误

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。

请您参考如下方法:

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()