更新 Django 中的一对多引用字段也会更新其他对象

Question

我有一个现有的数据库，其中包含两个表，称为身份和帐户，我正在尝试使用 Django ORM 对其进行管理。

Identities 与 Accounts 是一对多的关系，我将这两个表建模如下：

class Identity(models.Model):
    class Meta:
        managed = False
        db_table = "Identities"
    i_id = models.AutoField(db_column = "I_ID", primary_key = True) 
    name = models.CharField(db_column = "DisplayName", max_length = 200)

class Account(models.Model):
    class Meta:
        managed = False
        db_table = "Accounts"
    name = models.CharField(db_column = "Name", max_length = 200, primary_key = True)
    identity = models.ForeignKey("Identity", db_column = "I_ID", blank = True, null = True, related_name = "accounts")

我的问题是，当我更新与帐户关联的身份时，与新身份关联的所有帐户都会切换到新身份：

old_identity = Identity.objects.create(name = "Old")
new_identity = Identity.objects.create(name = "New")
account_1 = Account.objects.create(name = "account_1", identity = old_identity)
account_2 = Account.objects.create(name = "account_2", identity = old_identity)

# change the identity for account_1:
account_1.identity = new_identity
account_1.save()

# read account_2 from DB and check identity
account_2 = Account.objects.get(name = "account_2")

# identity is now "New" also for account_2!
print account_2.identity.name 

如果我直接在数据库中做同样的更新，只有我改的账号的身份发生了变化，并不是所有的账号都关联到了这个身份，所以这是Django引入的东西。

当我更改identity 字段时，我应该怎么做才能只更新一个帐户？

注意：为了清楚起见，数据库中的两个引用也都发生了变化，这不是数据未刷新或类似问题的问题。

Answer 1

从已发布的相关代码中检查问题。发布的代码按预期运行：

创建表格：

(venv)dani@egg-v3:~/tmp/lldldl/paolo$ python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: mytest
  Apply all migrations: admin, contenttypes, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Creating table mytest_identity
    Creating table mytest_account
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying sessions.0001_initial... OK

跑步：

(venv)dani@egg-v3:~/tmp/lldldl/paolo$ python manage.py shell
Python 2.7.3 (default, Feb 27 2014, 19:58:35) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from mytest.models import Account,Identity
>>> old_identity = Identity.objects.create(name = "Old")
>>> new_identity = Identity.objects.create(name = "New")
>>> account_1 = Account.objects.create(name = "account_1", 
                                       identity = old_identity)
>>> account_2 = Account.objects.create(name = "account_2", 
                                       identity = old_identity)
>>> 
>>> # change the identity for account_1:
>>> account_1.identity = new_identity
>>> account_1.save()
>>> 
>>> # read account_2 from DB and check identity
>>> account_2 = Account.objects.get(name = "account_2")
>>> 
>>> # identity is now "New" also for account_2!
>>> print account_2.identity.name 
Old
>>> 

用 django 1.7 和 sqlite3 测试。也许一些数据库触发器？后/预保存信号？