代码之家 › 专栏 › 技术社区 › twitu

在Django中保存模型而不写入数据库

many-to-many django-models database django python

twitu · 技术社区 · 7 年前

y/n 样式输入。问题是我无法创建不保存的对象,正如您在下面看到的那样。

>>> mov = Movie(name="completenothing")
>>> direc = Director(name="Someone")
>>> direc.movie_name.add(mov)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/username/Code/virtualenvironments/matrix/local/lib/python2.7/site-packages/django/db/models/fields/related_descriptors.py", line 513, in __get__
    return self.related_manager_cls(instance)
  File "/home/username/Code/virtualenvironments/matrix/local/lib/python2.7/site-packages/django/db/models/fields/related_descriptors.py", line 830, in __init__
    (instance, self.pk_field_names[self.source_field_name]))
ValueError: "<Director: Someone>" needs to have a value for field "id" before this many-to-many relationship can be used.
>>> direc.save()
>>> direc.movie_name.add(mov)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/username/Code/virtualenvironments/matrix/local/lib/python2.7/site-packages/django/db/models/fields/related_descriptors.py", line 934, in add
    self._add_items(self.source_field_name, self.target_field_name, *objs)
  File "/home/username/Code/virtualenvironments/matrix/local/lib/python2.7/site-packages/django/db/models/fields/related_descriptors.py", line 1060, in _add_items
    (obj, self.instance._state.db, obj._state.db)
ValueError: Cannot add "<Movie: completenothing N/A>": instance is on database "default", value is on database "None"
>>> mov.save()
>>> direc.movie_name.add(mov)

导演和电影处于多对多关系中,我希望在保存之前显示他们的信息。是否有某种机制允许这样做?

1 回复 | 直到 7 年前

Josewails 7 年前

如果你使用 pre_save 信号,你可以试试这个。

from django.db.models.signals import pre_save



def confirm_save(sender, instance, **kwargs):

    # do something with your instance (display information)  

    ans = input("Do you want to save(y/n)")


    if ans == 'y':
        print("Your instance saved successfully")

    else:
        raise Exception("Not saved")

pre_save.connect(confirm_save, sender=MyModel)

推荐文章

Nebula Tech · 在SQL Server中搜索字符串中单词的多次出现

1 年前

blogger13 · 视频租赁店数据库的规范化

1 年前

ashish · Postgres是否支持使用复合外键的“ON DELETE CASCADE”

1 年前

ì¤ì¤í · 为什么LEFT INNER JOIN被弃用?

1 年前

relatively_random · 确保两个表之间一致的共同参考

1 年前

Qi Xiang · Milvus在使用expr和vector进行搜索时是如何工作的?

1 年前

Grenish Rai · Firestore错误“用户文档不存在”

1 年前

Saijo-Shi · PLpgsql中的更新触发器

1 年前

Dante · Django::配置不当:池不支持持久连接

1 年前

YouLocalRUser · 删除重复行,保留第一行

1 年前