models.py

Question

我在Django Rest Framework上很新，而且我一直试图为我的一个模型编写一个序列化器。对于我的项目，我打算根据JSON API标准输出json结果，为此，我使用SerializerMethodField，我在其中调用方法get_data()，如下所示：

models.py

class Level(MPTTModel):
    name = models.CharField(max_length=100)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True)

    class MPTTMeta:
        order_insertion_by = ['name']


class Group(models.Model):
    name = models.CharField(max_length=100)
    level_set = models.ManyToManyField(Level, blank=True)

serializers.py

class LevelSerializer(serializers.ModelSerializer):
    data = serializers.SerializerMethodField()

    class Meta:
        model = Level
        fields = ('data',)

    def get_data(self, instance):
        return {
            "type": "Level",
            "uuid": instance.id_key(),
            "attributes": {
                "name": instance.name,
            },
            "relationships": {
                "children": self.get_children_recursive(),
            },
        }

    def get_children_recursive(self, child=None):
        """
        Generates a tree of levels structured according to JSON API standards.
        """
        if not child:
            children = self.instance.get_children()
            level = self.instance
        else:
            children = child.get_children()
            level = child
        tree = {
            'data': {
                'type': 'Level',
                'uuid': level.id_key(),
                'attributes': {
                    'name': level.name,
                },
                'relationships': {
                    'children': [],
                    'parents': [],
                }
            }
        }
        for child in children:
            tree['data']['relationships']['children'].append(self.get_children_recursive(child))
        return tree

class GroupSerializer(serializers.ModelSerializer):
    root_level_set = LevelSerializer(many=True)

    class Meta:
        model = Group
        fields = ('id_key', 'name', 'root_level_set')

奇怪的是，如果我转到shell并尝试序列化Level的实例，它可以正常工作，但是尝试序列化一个组会在get_children_recursive()处与if not child statement一致时出错}说'NoneType' object has no attribute 'get_children'。输出如下：

执行命令

from core.serializers import LevelSerializer
from core.models import Level
lvl = Level.objects.all()[0]
serializer = LevelSerializer(lvl)
print(serializer.data)

根据我按照JSON API标准设计的JSON结构输出嵌套级别及其子级别。

虽然如果我跑：

from core.serializers import GroupSerializer
from core.models import Group
grp = Group.objects.all()[0]
serializer = GroupSerializer(grp)
print(serializer.data)

输出：

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 503, in data
    ret = super(Serializer, self).data
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 239, in data
    self._data = self.to_representation(self.instance)
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 614, in to_representation
    self.child.to_representation(item) for item in iterable
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 614, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/serializers.py", line 472, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/home/maumau/.virtualenvs/olist/lib/python3.5/site-packages/rest_framework/fields.py", line 1653, in to_representation
    return method(value)
  File "/mnt/SHARED-DRIVE/Workspace/interview-tests/work-at-olist/core/serializers.py", line 20, in get_data
    "children": self.get_children_recursive(),
  File "/mnt/SHARED-DRIVE/Workspace/interview-tests/work-at-olist/core/serializers.py", line 29, in get_children_recursive
    children = self.instance.get_children()
AttributeError: 'NoneType' object has no attribute 'get_children'

对我来说似乎没有意义，Level it self的序列化拥有属性实例集，而Group的序列化也调用了Level的序列化。任何线索？

Answer 1

为什么要自己设计一切？让djrf做一些魔术：）

ReactNative.findNodeHandle(component)

为什么你的代码不起作用？因为错误的代码：

看看在这两种情况下调用class LevelSerializer(serializers.ModelSerializer): type = serializers.SerializerMethodField() attributes = serializers.SerializerMethodField() relationships = serializers.SerializerMethodField() def get_type(self, instance): return "Level" def get_attributes(self, instance): return { "name": instance.name } def get_relationships(self, instance): return { "children": self.__class__(instance.get_children(), many=True).data, "parents": [] } class Meta: model = Level fields = ('type', 'attributes', 'relationships') class GroupSerializer(serializers.ModelSerializer): level_set = LevelSerializer(many=True) class Meta: model = Group fields = ('name', 'level_set')有什么不同 - 一个参数 - LevelSerializer; many=True时 - 序列化程序没有many=True属性
旁边（1），第一次运行instance将第一个元素复制为第一个孩子
使用您的方法根本不需要get_children_recursive，因为所有操作都是手动完成的 - 在这种情况下，简单ModelSerializer会更好
通过创建虚拟Serializer字段 - 您使代码更复杂，为什么不直接使用数据来避免使用一个data密钥的字典

我的示例代码缺少data字段 - 您没有在此处记录，但添加它应该是一个breze

使用额外的模块id_key，可以简化代码：

rest_framework_recursive

Answer 2

serialzier中的属性名称：root_level_set。在模型中：level_set。

DRF尝试在组中查找属性root_level_set，找不到它并将其替换为None。这就是为什么你会遇到这样的错误。

修正：

重命名root_level_set - ＆gt;序列化程序中的level_set。
或将source添加到字段：root_level_set = LevelSerializer(source='level_set', many=True)

许多Django Rest Framework序列化生成序列化关系的NoneType实例

models.py

serializers.py

2 个答案: