python - 使用单个数据库表的 Django 模型继承 - 从父类(super class)访问子类的问题

Question

我正在使用 Oracle 开发 Django 应用程序，不允许修改数据库架构。 我有一个表，其中存在所有Thesis，它可以分为两个不相交的集合:PhdThesis 和BscMscThesis。我还有 Review 模型，它链接到 Thesis 数据库表，并且不关心它是 PhdThesis 还是 BscMscThesis >，所以我想将 Thesis 保留为 abstract = False 类。

class Thesis(models.Model):
    # Primary key  has to be specified explicite here for inheritance to work?
    id = models.DecimalField(db_column="ID", max_digits=10, decimal_places=0, primary_key=True)
    class Meta:
        db_table = "DZ_PRACE_CERT"
        managed = False

class Person(models.Model):
    class Meta:
        db_table = "MV_OSOBY"
        managed = False


class BscMscThesisManager(models.Manager):
    def get_query_set(self):
        return super(BscMscThesisManager, self).get_query_set().filter(personbscmscdiploma__isnull=False)

class BscMscThesis(Thesis):
    # needed for inheritance?
    thesis = models.OneToOneField(Thesis, db_column="ID", primary_key=True, parent_link=True)
    authors = models.ManyToManyField(Person, through="PersonBscMscDiploma", related_name='author_of_bsc_msc_theses')
    objects = BscMscThesisManager()

    class Meta:
        db_table = "DZ_PRACE_CERT"
        managed = False

class PersonBscMscDiploma(models.Model):
    bsc_msc_thesis = models.ForeignKey(BscMscThesis, db_column="PRC_CERT_ID")


class PhdThesisManager(models.Manager):
    def get_query_set(self):
        return super(PhdThesisManager, self).get_query_set().filter(personphddiploma__isnull=False)

class PhdThesis(Thesis):
    # needed for inheritance?
    thesis = models.OneToOneField(Thesis, db_column="ID", primary_key=True, parent_link=True)
    authors = models.ManyToManyField(Person, through="PersonPhdDiploma", related_name='author_of_phd_theses')
    objects = PhdThesisManager()

    class Meta:
        db_table = "DZ_PRACE_CERT"
        managed = False

class PersonPhdDiploma(models.Model):
    phd_thesis = models.ForeignKey(PhdThesis, db_column="PRC_CERT_ID")

我遇到的问题是:

>>> Thesis.objects.all()[0].phdthesis
<PhdThesis: Uniwersytecki System Obsługi Studiów. Parametryzowane filtry>
>>> Thesis.objects.all()[0].bscmscthesis
<BscMscThesis: Uniwersytecki System Obsługi Studiów. Parametryzowane filtry>
>>> Thesis.objects.all()[0].phdthesis.authors.all()
[]
>>> Thesis.objects.all()[0].bscmscthesis.authors.all()
[<Person: Jan1912 Kowalski1912>]
>>> Thesis.objects.all()[0].id
Decimal('903')
>>> BscMscThesis.objects.get(id=903)
<BscMscThesis: Uniwersytecki System Obsługi Studiów. Parametryzowane filtry>
>>> PhdThesis.objects.get(id=903)
DoesNotExist: PhdThesis matching query does not exist.

PhdThesis.objects.all() 和 BscMscThesis.objects.all() 按预期返回两个不相交的集合。

为什么在上面的例子中Thesis.objects.all()[0].phdthesis不返回None或DoesNotExist？我该怎么做才能得到这样的行为？

Answer 1

Django 似乎没有简单的方法来做到这一点。我最终实现了像 is_phd() 和 is_bsc_msc() 这样的方法，并像这样使用它们:

def get_absolute_url(self):
    if self.is_phd():
        return self.phdthesis.get_absolute_url()
    else:
        return self.bscmscthesis.get_absolute_url()