Django GenericRelation仍然无法从GenericForeignKey启用反向查询

Question

在我的Django项目中,我有一个名为ValueGenericForeignKey 的模型:

class Value(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE, blank=True, null=True)
    val_id = models.PositiveIntegerField(blank=True, null=True)
    data_obj = GenericForeignKey('content_type', 'val_id')

Value是一种多态表,它使用ContentType和GenericForeignKey来指向包含实际数据的任意表.例如,有一个模型Int,一个Value可以指向:

class Int(models.Model):
    data = models.IntegerField(blank=True, null=True)

因此,在创建一个实例后Int:

myint = Int.objects.create(data=1)

我可以创建一个Value指向它的:

myval = Value.objects.create(data_obj=myint)

还有其他同类机型,一个Value将指向,比如UInt,String和Float; 他们都只有一个领域data.但是,我想知道如何Value根据字段指向的模型包含的数据查询/过滤实例data_obj.即,我希望能够做到这样的事情:

Value.objects.filter(data_obj__data=1)

但这会导致错误:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/django/db/models/manager.py", line 122, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/django/db/models/query.py", line 790, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/django/db/models/query.py", line 808, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1243, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1269, in _add_q
    allow_joins=allow_joins, split_subq=split_subq,
  File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1149, in build_filter
    lookups, parts, reffed_expression = self.solve_lookup_type(arg)
  File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1035, in solve_lookup_type
    _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
  File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1316, in names_to_path
    "adding a GenericRelation." % name
FieldError: Field 'data_obj' does not generate an automatic reverse relation and therefore cannot be used for reverse querying. If it is a GenericForeignKey, consider adding a GenericRelation.

问题是即使我已经更新了每个数据模型以将GenericRelation字段返回到Value模型:

class Int(models.Model):
    data = models.IntegerField(blank=True, null=True)
    val_obj = GenericRelation(Value, object_id_field="val_id")

class UInt(models.Model):
    data = models.PositiveIntegerField(blank=True, null=True)
    val_obj = GenericRelation(Value, object_id_field="val_id")

class String(models.Model):
    data = models.CharField(max_length=2048)
    val_obj = GenericRelation(Value, object_id_field="val_id")

# etc.

我仍然无法进行反向查询工作并从上面得到相同的错误.我在这里做错了,添加GenericRelation仍然不允许反向查询或似乎改变任何东西？我肯定希望反向查询能够正常工作,因为项目有一个过滤脚本,Values如果我只能成功地反向查询,那么这个脚本会更容易上手.

更新:我想出了如何得不到FieldError,但仍然无法按照我想要的方式进行反向查询.我所做的就是添加related_query_name到每个的Int,UInt,Float等数据模型GenericRelation字段:

val_obj = GenericRelation(Value, object_id_field="val_id", related_query_name="val")

根据Django文档,我相信我会像这样反向查询:

Value.objects.filter(val__data=1)

然而,即使我确实有数据模型的数据字段包含int 1,这个和任何其他反向查询返回一个空列表.还有别的我做错了/丢失吗？

Answer 1

我有同样的问题,发现我必须related_query_name为每个相关模型定义一个唯一的,如下所述:

/sf/answers/2531665111/

例如:

class Int(models.Model):
    data = models.IntegerField(blank=True, null=True)
    val_obj = GenericRelation(Value, object_id_field="val_id",
                              related_query_name="int")

class UInt(models.Model):
    data = models.PositiveIntegerField(blank=True, null=True)
    val_obj = GenericRelation(Value, object_id_field="val_id",
                              related_query_name="uint")

class String(models.Model):
    data = models.CharField(max_length=2048)
    val_obj = GenericRelation(Value, object_id_field="val_id",
                              related_query_name="string")

然后,您将通过分别查询每个模型来创建过滤器,例如:

from django.db.models import Q

val = 1
val_filter = Q(int__data=val) | Q(uint__data=val) | Q(string__data=val)
filtered_values = Value.objects.filter(val_filter)

Answer 2

GenericRelation 不是一个实际的字段；无需向数据库添加任何内容；这不是你的错误的原因。

您可能需要将定义模型的应用程序添加到 INSTALLED_APPS 设置中。