Django Rest Framework：派生模型序列化器字段答案

【问题标题】：Django Rest Framework: Derived model serializer fieldsDjango Rest Framework：派生模型序列化器字段
【发布时间】：2018-06-07 18:58:09
【问题描述】：

我正在使用 Django Rest Framework 和 django-polymorphic-tree 构建一个树状分层数据库系统。我有两个模型——BaseTreeNode 和 DescriptionNode（后一个是从 BaseTreeNode 派生的）。具体来说，这是我的models.py：

class BaseTreeNode(PolymorphicMPTTModel):
    parent = PolymorphicTreeForeignKey('self', blank=True, null=True, related_name='children', verbose_name=_('parent'))
    title = models.CharField(_("Title"), max_length=200)

    def __str__(self):
        return "{}>{}".format(self.parent, self.title)

    class Meta(PolymorphicMPTTModel.Meta):
        verbose_name = _("Tree node")
        verbose_name_plural = _("Tree nodes")


# Derived model for the tree node:

class DescriptionNode(BaseTreeNode):
    description = models.CharField(_("Description"), max_length=200)

    class Meta:
        verbose_name = _("Description node")
        verbose_name_plural = _("Description nodes")

因此，每个title 字段（属于BaseTreeNode）都有一个关联的description 字段（属于DescriptionNode）。

现在，我想要的只是一个返回整个树的嵌套表示的 JSON。目前，我只定义了一个带有递归字段的简单序列化程序。我的序列化器.py

from rest_framework_recursive.fields import RecursiveField

class DescriptionNodeSerializer(serializers.ModelSerializer):
    class Meta:
        model = DescriptionNode
        fields = ('description',)

class BaseTreeNodeSerializer(serializers.ModelSerializer):
    subcategories = serializers.ListSerializer(source="children",child=RecursiveField())  
    class Meta:
        model = BaseTreeNode
        fields = ('id', 'title', 'subcategories')

这给了我（仅适用于 BaseTreeNodeSerializer）：

[
  {
    "id": 1,
    "title": "Apple",
    "subcategories": [
      {
        "id": 2,
        "title": "Contact Person",
        "subcategories": []
      },
      {
        "id": 3,
        "title": "Sales Stage",
        "subcategories": [
          {
            "id": 4,
            "title": "Suspecting",
            "subcategories": [
              {
                "id": 5,
                "title": "Contact verification",
                "subcategories": []
              }
            ]
          },
          {
            "id": 6,
            "title": "Prospecting",
            "subcategories": [
              {
                "id": 7,
                "title": "Client Detail",
                "subcategories": []
              }
            ]
          }
        ]
      },
      {
        "id": 9,
        "title": "Medium",
        "subcategories": [
          {
            "id": 10,
            "title": "Status",
            "subcategories": []
          }
        ]
      },
      {
        "id": 13,
        "title": "Remainder",
        "subcategories": []
      }
    ]
  }
]

我的问题是，如何在层次结构中包含与每个 title 字段（来自 BaseTreeNode 模型）相关联的 description 字段（来自派生模型）？比如：

... {
                "id": 5,
                "title": "Contact verification",
                "description": "Verified"
                "subcategories": []
              } ...

【问题讨论】：

标签： python django hierarchical-data derived-class django-polymorphic

【解决方案1】：

对应的模型如下：

class DescriptionNode(BaseTreeNode):
    basetreenode = models.OneToOneField(BaseTreeNode, related_name="base_tree")
    description = models.CharField(_("Description"), max_length=200)

    class Meta:
        verbose_name = _("Description node")
        verbose_name_plural = _("Description nodes")

序列化器如下：

from rest_framework_recursive.fields import RecursiveField

class BaseTreeNodeSerializer(serializers.ModelSerializer):
    description = serializers.SerializerMethodField()
    subcategories = serializers.ListSerializer(source="children",child=RecursiveField())

    class Meta:
        model = BaseTreeNode
        fields = ('id', 'title', 'description', 'subcategories')

    def get_description(self, obj):
        return obj.base_tree.description #base_tree is related name of basetreenode field

【讨论】：

是的！像魅力一样工作（几乎）。 “django.db.utils.IntegrityError: UNIQUE constraint failed”的问题仍然存在，通过删除并重新运行迁移来解决。干杯！