django模型递归导入 - 如何解决

Question

我有一个模型project_phase:

    from django.db import models
    from django.utils import simplejson
    from core.models import pmo_review_task

它引用了pmo_review_task(因为它在其save ovewrite中创建了一个pmo_review_task)

from django.db import models
from datetime import datetime
from django.contrib.auth.models import User
from core.models import sc_review_task

引用引用project_phase的sc_review_task(因为它在save ovewrite中创建了project_phase)

from django.db import models
from core.models import project_phase

所以它结束了project_phase导入pmo_review_task导入sc_review_task导入project_phase,我想它会以某种方式循环生成这个错误:

Unhandled exception in thread started by <bound method Command.inner_run of <django.core.management.commands.runserver.Command object at 0x010ACFB0>>
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\django\core\management\commands\runserver.py", line 88, in inner_run
    self.validate(display_num_errors=True)
  File "C:\Python27\lib\site-packages\django\core\management\base.py", line 249, in validate
    num_errors = get_validation_errors(s, app)
  File "C:\Python27\lib\site-packages\django\core\management\validation.py", line 35, in get_validation_errors
    for (app_name, error) in get_app_errors().items():
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 146, in get_app_errors
    self._populate()
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 64, in _populate
    self.load_app(app_name)
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 78, in load_app
    models = import_module('.models', app_name)
  File "C:\Python27\lib\site-packages\django\utils\importlib.py", line 35, in import_module
    __import__(name)
  File "C:\work\Portman\core\models\__init__.py", line 4, in <module>
    from pmo_review_task import pmo_review_task
  File "C:\work\Portman\core\models\pmo_review_task.py", line 5, in <module>
    from core.models import sc_review_task
  File "C:\work\Portman\core\models\sc_review_task.py", line 3, in <module>
    from core.models import project_phase
  File "C:\work\Portman\core\models\project_phase.py", line 4, in <module>
    from core.models import pmo_review_task
ImportError: cannot import name pmo_review_task

我怎么克服这个？

Answer 1

两种方式:

1. 在方法中导入模型(如@YujiTomita建议).

2. 使用为懒惰模型导入设计的get_model函数django.db.models:

   project_phase = get_model('core', 'project_phase')
   

我更喜欢第二个,但两种方法都可以.

Answer 2

导入方法project_phase内部save.

只要执行代码,就会调用导入.

如果它位于全局模块命名空间(顶部),则会立即调用它,并且您将描述循环导入问题,因为一个文件导入另一个导入原始文件的文件.

如果将问题import语句放在函数中,则在导入文件时会/不/调用它.

import foo # executed upon importing this file. 

def import_foo_when_called():
    import foo # only executed when function is called, thus no problems when 
               # another module imports this file.