python - 如何在 django oscar 的策略中应用可变税？

Question

我正在为印度开展一个奥斯卡项目，现在我想对产品征税。 我已按照文档对 prices and availability 征税， fork 了合作伙伴应用程序。当我指定rate=('0.20')时，它对所有产品征收20%的税，现在我想让它动态化。

所以我浏览了strategy.FixedRateTax的代码，并尝试实现get_rate()的代码，因为所有产品都会调用它。

我想要使其动态的方式是，根据我想要对 get_rate() 中的产品应用税的产品类别。

所以我在 core/models.py 中创建了一个模型

class CategoryTax(models.Model):
    category = models.OneToOneField(Category, on_delete=models.CASCADE, unique=True)
    gst_tax = models.DecimalField(max_digits=11, decimal_places=4, null=True, default=0)

    def __str__(self):
        return "%s" % self.category

这里类别模型的导入工作正常，但是当我转到strategy.py并从核心和其他应用程序导入模型时，django给出了异常(exception)。

我的 forked_apps/partner/strategy.py 是:

from decimal import Decimal as D
from oscar.apps.partner import strategy, prices
from django.conf import settings

from oscar.core.loading import get_model
from core.models import CategoryTax

Partner = get_model('partner', 'Partner')
Category = get_model('catalogue', 'Category')
Product = get_model('catalogue', 'Product')
ProductCategory = get_model('catalogue', 'ProductCategory')


class Selector(object):
    """
    Custom selector to return a India-specific strategy that charges GST
    """

    def strategy(self, request=None, user=None, **kwargs):
        return IndiaStrategy()


class IncludingVAT(strategy.FixedRateTax):
    """
    Price policy to charge VAT on the base price
    """
    # We can simply override the tax rate on the core FixedRateTax.  Note
    # this is a simplification: in reality, you might want to store tax
    # rates and the date ranges they apply in a database table.  Your
    # pricing policy could simply look up the appropriate rate.

    # The Tax rate applied here is 3 % GST Now
    rate = D(settings.SITE_GST)

    def get_rate(self, product, stockrecord):
        """
        This method serves as hook to be able to plug in support for varying tax rates
        based on the product.

        TODO: Needs tests.
        """

        try:
            product = Product.objects.get(id=product.id)
            prod_cat = ProductCategory.objects.get(product=product)
            cat = Category.objects.get(id=prod_cat.category_id)

            cat_tax = CategoryTax.objects.get(category=cat)
            print("The Cat Tax: ", cat_tax)

        except Exception as e:
            print(e)
        return self.rate
class IndiaStrategy(strategy.UseFirstStockRecord, IncludingVAT,
             strategy.StockRequired, strategy.Structured):
    """
    Typical India strategy for physical goods.

    - There's only one warehouse/partner so we use the first and only stockrecord
    - Enforce stock level.  Don't allow purchases when we don't have stock.
    - Charge Indian GST on prices.  Assume everything is standard-rated.
    """

我得到的异常是:

django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.

还有:ImportError:无法导入名称“CategoryTax”

请向我建议任何可以用来完成这项工作的方法。

我正在使用 Django 2.1.3、Django Oscar 1.6.4

整个错误堆栈跟踪:

Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0x7f623e655400>
Traceback (most recent call last):
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 296, in get_model
    return apps.get_model(app_label, model_name)
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 195, in get_model
    self.check_models_ready()
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 137, in check_models_ready
    raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 296, in get_model
    return apps.get_model(app_label, model_name)
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 195, in get_model
    self.check_models_ready()
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 137, in check_models_ready
    raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/venvs/test/lib/python3.6/site-packages/django/utils/autoreload.py", line 225, in wrapper
    fn(*args, **kwargs)
  File "/home/test/abhushan/lib/python3.6/site-packages/django/core/management/commands/runserver.py", line 109, in inner_run
    autoreload.raise_last_exception()
  File "/home/venvs/test/lib/python3.6/site-packages/django/utils/autoreload.py", line 248, in raise_last_exception
    raise _exception[1]
  File "/home/venvs/test/lib/python3.6/site-packages/django/core/management/__init__.py", line 337, in execute
    autoreload.check_errors(django.setup)()
  File "/home/venvs/test/lib/python3.6/site-packages/django/utils/autoreload.py", line 225, in wrapper
    fn(*args, **kwargs)
  File "/home/venvs/test/lib/python3.6/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 112, in populate
    app_config.import_models()
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "/home/venvs/test/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/venvs/test/project/core/models.py", line 8, in <module>
    Category = get_model('catalogue', 'Category')
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 308, in get_model
    import_module('%s.%s' % (app_config.name, MODELS_MODULE_NAME))
  File "/home/venvs/test/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/apps/catalogue/models.py", line 4, in <module>
    from oscar.apps.catalogue.abstract_models import *  # noqa
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/apps/catalogue/abstract_models.py", line 35, in <module>
    Selector = get_class('partner.strategy', 'Selector')
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 59, in get_class
    return get_classes(module_label, [classname], module_prefix)[0]
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 69, in get_classes
    return class_loader(module_label, classnames, module_prefix)
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 141, in default_class_loader
    local_module = _import_module(local_module_label, classnames)
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 182, in _import_module
    return __import__(module_label, fromlist=classnames)
  File "/home/test/forked_apps/partner/strategy.py", line 16, in <module>
    Category = get_model('catalogue', 'Category')
  File "/home/venvs/test/lib/python3.6/site-packages/oscar/core/loading.py", line 311, in get_model
    return apps.get_registered_model(app_label, model_name)
  File "/home/venvs/test/lib/python3.6/site-packages/django/apps/registry.py", line 270, in get_registered_model
    "Model '%s.%s' not registered." % (app_label, model_name))
LookupError: Model 'catalogue.Category' not registered.

Answer 1

您的循环导入导致此操作失败。在 strategy.py 中，您尝试加载 Category 模型，而在 Oscar 的 catalogue/abstract_models.py 中，它又尝试加载Selector 模型(出于我不清楚的原因 - 认为这实际上是一个错误，并将单独研究它)。

我认为如果您将 selector.py 中的导入移动到需要它们的方法内部，它应该可以工作:

def get_rate(self, product, stockrecord):
    Category = get_model('catalogue', 'Category')
    Product = get_model('catalogue', 'Product')
    ProductCategory = get_model('catalogue', 'ProductCategory')
    # do your logic here