Django 继承，class 依赖 directly/indirectly 的 class 之间的关系

Question

我不明白是否可以使用使用共享实例的模型之间的关系，例如我有一个 过程模型 使用 class 调用 Area，而这个 class ( Area) 用于 发票模型 需要 [= 的实例29=]ConceptDetail 并且它需要 区域 class，但是 过程class依赖于Invoice的实例，所以程序class使用区域class和发票class.

我的图表示例

Procedure (depends of) Area, Invoice

Invoice (depends of) ConceptDetail (who depends of) Area

当我尝试这个时，我得到一个 ImportError: cannot import name 'Area' ，如果我删除 Procedure 和 Invoice 的关系它工作正常，这是我的错误，关系创建？，我想我的修复是创建一个新的区域class 对于ConceptDetail class，不好的是里面的数据会重复，觉得这样不对吧？

这是我的代码

# from procedure models.py 
from invoice.model import Invoice
class Area(CreateUpdateMixin):
    name = models.CharField(max_length=75, verbose_name=_('Area'))
    renovated = models.BooleanField(default=False)
    requested = models.BooleanField(default=False)
def __str__(self):
    return self.name

class Meta:
    verbose_name = _('Area')
    verbose_name_plural = _('Areas')

class Procedure(CreateUpdateMixin):

    title = models.CharField(max_length=150, verbose_name=_('Titulo'))
    area = models.ForeignKey(Area, verbose_name=_('Area'), related_name='areas')
    figure = models.ForeignKey(Figure, verbose_name=_('Figura'), blank=True, null=True)
    linked = models.ManyToManyField("self", verbose_name=_('Relacionados'), blank=True)

    # invoices.invoice
    invoices = models.ManyToManyField(Invoice, verbose_name=_('Facturas'), blank=True)

# from invoice models.py
from procedure.models import Area
class ConceptDetail(CreateUpdateMixin):
    name = models.CharField(max_length=150)
    area = models.ForeignKey(Area, verbose_name=_('Aplica al Area'))
    concept = models.CharField(max_length=150)
    fee = models.FloatField()
    duty = models.FloatField()

class Invoice(CreateUpdateMixin):

    #
    invoice = models.CharField(max_length=15, verbose_name=_('Número de Factura'))
    date = models.DateField(verbose_name=_('Fecha'))  # YYYYMMDD
    status = models.ForeignKey(StatusInvoice, null=True, blank=True)

来自 session invoice_detail = models.ManyToManyField（发票详细信息，空白=真）

# from settings.py
INSTALLED_APPS = (
    'procedure',
    'invoice',
)

它破坏了我的应用程序这是错误：

> Traceback (most recent call last):
  File "/Applications/PyCharm.app/Contents/helpers/pycharm/django_manage.py", line 41, in <module>
    run_module(manage_file, None, '__main__', True)
  File "/usr/local/Cellar/python3/3.4.3/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 182, in run_module
    return _run_module_code(code, init_globals, run_name, mod_spec)
  File "/usr/local/Cellar/python3/3.4.3/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/usr/local/Cellar/python3/3.4.3/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Volumes/iMac/Users/paridin/Devel/python/pyppm/manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/site-packages/django/core/management/__init__.py", line 312, in execute
    django.setup()
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/site-packages/django/__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/site-packages/django/apps/registry.py", line 108, in populate
    app_config.import_models(all_models)
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/site-packages/django/apps/config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "/Volumes/iMac/Users/paridin/.virtualenvs/pyppm/lib/python3.4/importlib/__init__.py", line 109, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 2254, in _gcd_import
  File "<frozen importlib._bootstrap>", line 2237, in _find_and_load
  File "<frozen importlib._bootstrap>", line 2226, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1200, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1129, in _exec
  File "<frozen importlib._bootstrap>", line 1471, in exec_module
  File "<frozen importlib._bootstrap>", line 321, in _call_with_frames_removed
  File "/Volumes/iMac/Users/paridin/Devel/python/pyppm/registration/models.py", line 4, in <module>
    from procedure.models import Area
  File "/Volumes/iMac/Users/paridin/Devel/python/pyppm/procedure/models.py", line 8, in <module>
    from invoice.models import Invoice
  File "/Volumes/iMac/Users/paridin/Devel/python/pyppm/invoice/models.py", line 5, in <module>
    from procedure.models import Area
ImportError: cannot import name 'Area'

Answer 1

您正在通过在 procedure/models.py 中导入 from invoice.model import Invoice 和在 invoice/models.py 中导入 from procedure.models import Area 来进行循环导入。

像这样更改您的代码：

# procedure/models.py:
class Procedure(CreateUpdateMixin):
    ...
    # invoices.invoice as a string:
    invoices = models.ManyToManyField('invoice.Invoice', 
                                       verbose_name=_('Facturas'), blank=True)

主要概念是将 class 引用更改为字符串。它使循环依赖成为可能。您也可以在 invoice/models.py 中执行此操作。

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