场景：我有一个模型，被其它多个模型关联，我配置了CASCADE级联删除，我想要告知用户删除该实例之后，哪些关联数据将会被一同删除。

假设我们当前有这样一组模型：

class Warehouse(models.Model):
    """仓库"""
    ...
    
    
class OutboundRecord(models.Model):
    """出库单"""
    warehouse = models.ForeignKey('Warehouse', on_delete=models.CASCADE, verbose_name="仓库")
    ...
    
    
class OutboundList(models.Model):
    """出库单明细"""
    warehouse = models.ForeignKey('Warehouse', on_delete=models.CASCADE, verbose_name="仓库")
    ...


class InboundRecord(models.Model):
    """入库单"""
    warehouse = models.ForeignKey('Warehouse', on_delete=models.CASCADE, verbose_name="仓库")
    ...


class InboundList(models.Model):
    """入库明细"""
    warehouse = models.ForeignKey('Warehouse', on_delete=models.CASCADE, verbose_name="仓库")
    ...

它们的关系如下:

想要查询warehouse所有关联数据的方法很简单，具体代码如下：

from django.contrib.admin.utils import NestedObjects
from xxx import Warehouse

o = NestedObjects(using='default')
o.collect(Warehouse.object.all())
print(o.nest())

假设我们事先已经插入了一些数据，上述代码会输出一个嵌套数组结构，所有的关系一目了然，嵌套数组的处理也很轻松，根据你的需要进行递归遍历即可。

[
  <Warehouse: 仓库1>,
  [
    <OutboundRecord: OutboundRecord object (2)>,
    [
      <OutboundList: OutboundList object (2)>,
      <OutboundList: OutboundList object (5)>,
      <OutboundList: OutboundList object (8)>
    ],
    <OutboundRecord: OutboundRecord object (3)>,
    [
      <OutboundList: OutboundList object (3)>,
      <OutboundList: OutboundList object (6)>,
      <OutboundList: OutboundList object (9)>
    ],
    <InboundRecord: InboundRecord object (1)>,
    [
      <InboundList: InboundList object (1)>,
      <InboundList: InboundList object (4)>,
      <InboundList: InboundList object (7)>
    ]
  ],
  <Warehouse: 仓库2>,
  [
    <OutboundRecord: OutboundRecord object (1)>,
    [
      <OutboundList: OutboundList object (1)>,
      <OutboundList: OutboundList object (4)>,
      <OutboundList: OutboundList object (7)>
    ],
    <InboundRecord: InboundRecord object (2)>,
    [
      <InboundList: InboundList object (2)>,
      <InboundList: InboundList object (5)>,
      <InboundList: InboundList object (8)>
    ],
    <InboundRecord: InboundRecord object (3)>,
    [
      <InboundList: InboundList object (3)>,
      <InboundList: InboundList object (6)>,
      <InboundList: InboundList object (9)>
    ]
  ],
  <Warehouse: 仓库3>
]

NestedObjects的collect方法来自父类Collector，不过NestedObjects中多来nest()方法帮我们构建方便的层级结构。