Django-MPTT叶子节点有多种类型

Question

我正在开发一个hirerchical应用程序,其中叶节点可以是不同模型的实例.我无法弄清楚如何使它与django-mptt应用程序一起工作.这个应用程序甚至可以实现吗？如果是的话,我做错了什么？如果没有,那里有什么我想做什么？

以下是模型的基本结构:

class FolderItemBase(MPTTModel):
    order = models.PositiveIntegerField()

    class Meta:
        abstract = True

    class MPTTMeta:
        parent_attr = 'folder'
        order_insertion_by = ['order']

class Folder(FolderItemBase):
    folder = TreeForeignKey('Folder', related_name='folders', blank=True, null=True)
    ...

class Image(FolderItemBase):
    folder = TreeForeignKey('Gallery', related_name='images') # cannot be null since leaf has to be inside of a folder
    ...

当我尝试执行以下操作时,我只能获取"文件夹"子项,而没有任何图像.当我试图获得图像的祖先时也是如此

>>> folder1 = Folder.objects.create(title='Folder 1', order=0)
>>> folder2 = Folder(title='Folder 2', order=0)
>>> folder2.insert_at(folder1, save=True)
>>> image = Image(...)
>>> image.insert_at(folder1, save=True)
>>> folder1.get_children()
[<Folder: Folder 2>]
>>> image.get_ancestores()
[]

这就是在所有这些之后事物存储在数据库中的方式:

Folder table
----------------
+----+-------+-----+------+---------+-------+-----------+----------+
| ID | order | lft | rght | tree_id | level | folder_id | title    |
+----+-------+-----+------+---------+-------+-----------+----------+
| 1  | 0     | 1   | 4    | 1       | 0     |           | Folder 1 |
+----+-------+-----+------+---------+-------+-----------+----------+
| 2  | 0     | 2   | 3    | 1       | 1     | 1         | Folder 2 |
+----+-------+-----+------+---------+-------+-----------+----------+

Images Table
------------
+----+-------+-----+------+---------+-------+-----------+
| ID | order | lft | rght | tree_id | level | folder_id |
+----+-------+-----+------+---------+-------+-----------+
| 1  | 1     | 2   | 3    | 1       | 1     | 1         |
+----+-------+-----+------+---------+-------+-----------+

正如你可以看到它的数字应该是什么形象和正确的级别数(在至少这似乎是)左右的数字但它不那么然后更新文件夹表格什么,当你尝试做一个查询什么都没有被选中.

任何指针都表示赞赏.谢谢.

Answer 1

AFAIK,这是不可能的; django-mptt支持Django的QuerySet,它只能用于某种类型的东西.您可以使用contenttypes框架将"真实"项与类似的内容相关联FolderItem,这些内容仅用于层次结构,例如

from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class FolderItem(MPTTModel):
    folder = TreeForeignKey('Folder', related_name='folders', blank=True, null=True
    order = models.PositiveIntegerField()
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

    class Meta:
        abstract = True

    class MPTTMeta:
        parent_attr = 'folder'
        order_insertion_by = ['order']

然后,当您使用django-mptt管理器方法等时,您将获得FolderItems的查询集,并且可以通过通用外键在遍历集合时访问Folder/ Image为每个.

但是,请注意,这在数据库查询方面可能会很昂贵,因为每次访问通用外键时,都必须发出新的查询.