删除相关模型django

Question

我目前有这个模型我如何删除徽标，而不删除公司model.Please示例代码，如果可能的话谢谢。

class Picture(models.Model): 
    owner = models.ForeignKey(User,blank = True) 
    caption = models.CharField(max_length=150, blank=True, null=True) 
    image = ImageField(upload_to='images/',blank = True, null = True) 

class Company(GenericUser): 
    company_name = models.CharField(max_length=150,blank = True,null = True) 
    logo = models.ForeignKey(Picture,blank = True,null = True) 

这是一个模型，我将如何从土地模型中删除照片模型看起来像这样。

class Land(Properies): 
    photo = models.ManyToManyField(Picture,blank=True,related_name='Land_Pictures',null = True) 

我想这一点是没有作用

checked_list = [] 
start = 1    
land_photos = sorted(list(land.photo.select_related()),reverse =True) 
while start < 8: 
    photo = 'photo%s' % start 
    checked = form.cleaned_data[photo] 
    if checked != None: 
     checked_list.append(land_photos[start - 1]) 
     start += 1    
for a_foto in checked_list: 
land.photo.remove(a_foto) 
try: 
    a_foto.remove_all_file() 
    a_foto.delete() 
except OSError: 
    pass 

我不断收到这样的ID错误设置为none，如果我打刷新它的作品，我认为

Exception Type:  AssertionError 
Exception Value:  
Picture object can't be deleted because its id attribute is set to None. 

Answer 1

改变你的公司模式是这样的：

class Company(GenericUser): 
    company_name = models.CharField(max_length=150,blank = True,null = True) 
    logo = models.ForeignKey(Picture,blank = True,null = True, on_delete=models.SET_NULL) 

文档：https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ForeignKey.on_delete

Answer 2

是否有任何理由：

a）您正在使用(GenericUser)？这无疑会造成你的问题。

b）不能只是删除属性（每下），然后迁移数据？

class Picture(models.Model): 
    owner = models.ForeignKey(User,blank = True) 
    caption = models.CharField(max_length=150, blank=True, null=True) 
    image = ImageField(upload_to='images/',blank = True, null = True) 

class Company(models.Model): 
    company_name = models.CharField(max_length=150, blank=True, null=True) 
    logo = models.ForeignKey(Picture, blank=True, null=True) 

或者是你想在这里每删除一个相关的例子： https://docs.djangoproject.com/en/dev/ref/models/relations/#django.db.models.fields.related.RelatedManager.remove

在这种情况下，你会使用remove()。

Answer 3

您有任何公司反对图片以清除引用对象要删除。

logo = company.logo 
company.logo = None 
logo.delete() 

但是，如果图片是由多个公司引用，试试这个：

logo = Picture.object.get(...) # the Picture you want to delete 
logo.company_set.update(logo=None) 
logo.delete() 

你也应该考虑改变公司从该参考图像，以便相关情况没有得到默认情况下删除。

class Company(GenericUser): 
    company_name = models.CharField(max_length=150,blank = True,null = True) 
    logo = models.ForeignKey(Picture,blank = True,null = True, on_delete=models.SET_NULL)