Django相关模型无法解析

Question

我有两个 django/python 应用程序，一个在 Django 1.8 和 Python 3.4 上运行，另一个在 Django 1.8 和 Python 2.7 上运行。这些应用程序共享一个数据库并使用一个 python 包，该包包含在几个不同应用程序中的两个应用程序之间共享的多个模型。

在 3.4 上运行的应用程序工作正常，但在 2.7 上运行的应用程序会抛出 ValueError: Relate Model 'model_reference' 无法解析。

在这个伪示例中，包是 core_app，这两个模型位于 core_app 中包含的名为 foobar 和 barfoo 的单独应用程序中。

foob​​ar/models.py

class Model_A(models.Model):
   name = TextField()

barfoo/models.py

class Model_B(models.Model):
   model_a = ForeignKey('core_app_foobar.Model_A')

这是完整的堆栈跟踪。

    /home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/manager.pyc in manager_method(self, *args, **kwargs)
    125         def create_method(name, method):
    126             def manager_method(self, *args, **kwargs):
--> 127                 return getattr(self.get_queryset(), name)(*args, **kwargs)
    128             manager_method.__name__ = method.__name__
    129             manager_method.__doc__ = method.__doc__

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/query.pyc in get(self, *args, **kwargs)
    326         if self.query.can_filter():
    327             clone = clone.order_by()
--> 328         num = len(clone)
    329         if num == 1:
    330             return clone._result_cache[0]

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/query.pyc in __len__(self)
    142 
    143     def __len__(self):
--> 144         self._fetch_all()
    145         return len(self._result_cache)
    146 

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/query.pyc in _fetch_all(self)
    963     def _fetch_all(self):
    964         if self._result_cache is None:
--> 965             self._result_cache = list(self.iterator())
    966         if self._prefetch_related_lookups and not self._prefetch_done:
    967             self._prefetch_related_objects()

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/query.pyc in iterator(self)
    236         # Execute the query. This will also fill compiler.select, klass_info,
    237         # and annotations.
--> 238         results = compiler.execute_sql()
    239         select, klass_info, annotation_col_map = (compiler.select, compiler.klass_info,
    240                                                   compiler.annotation_col_map)

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in execute_sql(self, result_type)
    827             result_type = NO_RESULTS
    828         try:
--> 829             sql, params = self.as_sql()
    830             if not sql:
    831                 raise EmptyResultSet

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in as_sql(self, with_limits, with_col_aliases, subquery)
    376         refcounts_before = self.query.alias_refcount.copy()
    377         try:
--> 378             extra_select, order_by, group_by = self.pre_sql_setup()
    379             if with_limits and self.query.low_mark == self.query.high_mark:
    380                 return '', ()

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in pre_sql_setup(self)
     46         might not have all the pieces in place at that time.
     47         """
---> 48         self.setup_query()
     49         order_by = self.get_order_by()
     50         extra_select = self.get_extra_select(order_by, self.select)

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in setup_query(self)
     37         if all(self.query.alias_refcount[a] == 0 for a in self.query.tables):
     38             self.query.get_initial_alias()
---> 39         self.select, self.klass_info, self.annotation_col_map = self.get_select()
     40         self.col_count = len(self.select)
     41 

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in get_select(self)
    185         if self.query.default_cols:
    186             select_list = []
--> 187             for c in self.get_default_columns():
    188                 select_list.append(select_idx)
    189                 select.append((c, None))

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/sql/compiler.pyc in get_default_columns(self, start_alias, opts, from_parent)
    522             alias = self.query.join_parent_model(opts, model, start_alias,
    523                                                  seen_models)
--> 524             column = field.get_col(alias)
    525             result.append(column)
    526         return result

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in get_col(self, alias, output_field)
   2015 
   2016     def get_col(self, alias, output_field=None):
-> 2017         return super(ForeignKey, self).get_col(alias, output_field or self.related_field)
   2018 
   2019 

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in related_field(self)
   1895     @property
   1896     def related_field(self):
-> 1897         return self.foreign_related_fields[0]
   1898 
   1899     def get_reverse_path_info(self):

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in foreign_related_fields(self)
   1629     @property
   1630     def foreign_related_fields(self):
-> 1631         return tuple(rhs_field for lhs_field, rhs_field in self.related_fields)
   1632 
   1633     def get_local_related_value(self, instance):

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in related_fields(self)
   1616     def related_fields(self):
   1617         if not hasattr(self, '_related_fields'):
-> 1618             self._related_fields = self.resolve_related_fields()
   1619         return self._related_fields
   1620 

/home/ubuntu/moi/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in resolve_related_fields(self)
   1601             raise ValueError('Foreign Object from and to fields must be the same non-zero length')
   1602         if isinstance(self.rel.to, six.string_types):
-> 1603             raise ValueError('Related model %r cannot be resolved' % self.rel.to)
   1604         related_fields = []
   1605         for index in range(len(self.from_fields)):

ValueError: Related model 'core_app_foobar.Model_A' cannot be resolved

Answer 1

尝试一下：

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class Model_B(models.Model):\n   model_a = ForeignKey(\'foobar.Model_A\')\n

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不要忘记继承 django 模型。（两个都）

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from django.db import models\n

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要引用另一个应用程序中定义的模型，您可以显式\n 指定具有完整应用程序标签的模型。例如，如果上面的制造商模型是在另一个称为生产的应用程序中定义的，则您\xe2\x80\x99d 需要使用：

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外键文档

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