Question

我有以下概念模型：

class GenericAbstractBase(models.Model):
    name = models.CharField(max_length=255)
    staff = generic.GenericRelation(
        "Staff",
        content_type_field="content_type",
        object_id_field="object_id",
    )

    class Meta:
        abstract = True


class GenericModelA(GenericAbstractBase):
    extra_a = models.CharField(max_length=255)


class GenericModelB(GenericAbstractBase):
    extra_b = models.CharField(max_lenth=10)


class Staff(models.Model):

    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    active = models.CharField(max_length=10, choices = ACTIVE_CHOICES)

    limit = models.Q(app_label='staff', model='genericmodela') | models.Q(app_label='staff', model='genericmodelb')
    content_type = models.ForeignKey(ContentType, limit_choices_to=limit)
    object_id = models.PositiveIntegerField()
    generic_object = generic.GenericForeignKey("content_type", "object_id")

在Django v1.4＆amp; Django v1.5以下查询工作正常：

>>> ctype = ContentType.objects.get_for_model(GenericModelA)
>>> Staff.objects.filter(
        content_type=ctype,
        genericmodela__name__icontains="a"
    )
>>> [<Staff: Abbott, Kaylee>, <Staff: Adams, Kay>, ... ]

它生成的SQL（sqlite）看起来像：

SELECT 
    "staff_staff"."id", "staff_staff"."first_name","staff_staff"."last_name",
"staff_staff"."active","staff_staff"."content_type_id" ,"staff_staff"."object_id"
FROM "staff_staff"
INNER JOIN "staff_staff" T2 ON ("staff_staff"."id" = T2."id")
INNER JOIN "staff_genericmodela" ON (T2."object_id" = "staff_genericmodela"."id")
WHERE (
"staff_genericmodela"."name" LIKE % a % ESCAPE \ '\\\'
AND "staff_staff"."content_type_id" = 11
)

但是在Django 1.6中，查询失败并出现FieldError：

FieldError: Cannot resolve keyword 'genericmodela' into field. Choices are: active, content_type, department, first_name, id, last_name, object_id, position

以下陈述in the release notes可能相关：

Django 1.6包含对ORM的许多更改。这些变化大多分为三类：


错误修复（例如，通用关系的正确连接子句，查询组合，联接提升和连接修剪修复）

我的问题是，Django 1.6中发生了什么变化导致这种情况破裂？我是否坚持使用extra或在Python中进行此类过滤？

Answer 1

我找到了一些interesting information here。

作为一种解决方法，您可以执行以下操作：

ctype = ContentType.objects.get_for_model(GenericModelA)

pk_list = Staff.objects.filter(
    content_type=ctype
).values_list('object_id', flat=True)

GenericModelA.objects.filter(pk__in=pk_list, name__icontains="a")

Answer 2

由于未记录的行为，这似乎仅适用于Django 1.4，因此我决定在CASE查询中使用extra语句来执行我想要的查询。例如：

cta = ContentType.objects.get_for_model(models.GenericModelA)
ctb = ContentType.objects.get_for_model(models.GenericModelB)

extraq = """
CASE
    WHEN content_type_id = {0}
        THEN (SELECT extra_a from staff_genericmodela WHERE object_id = staff_genericmodela.id)
    WHEN content_type_id = {1}
        THEN (SELECT extra_b from staff_genericmodelb WHERE object_id = staff_genericmodelb.id)
 END
 """.format(cta.pk, ctb.pk)

 Staff.objects.extra(select={'genericname': extraq}).extra(where=["genericname LIKE %s", params=["%{0}%".format("foobar")])

到目前为止，这对我来说效果很好，应该可以轻松扩展到其他类似案例。

Django通用外键过滤（v1.5和v1.6之间的区别）

2 个答案: