相关模型的只读字段没有出现，使用 Django Rest Framework？

Question

我有两个模型（和一个抽象模型）：用户、法师和角色。来自 Character.

的法师 'inherits'

角色有一个 updated_date 字段，我正在尝试查看用户法师更新的最新日期：

class UserSerializer(serializers.ModelSerializer):
    mage_by_user = serializers.PrimaryKeyRelatedField(
        many=True, queryset=Mage.objects.all())
    mage_last_updated = serializers.ReadOnlyField(
        source='mage_by_user.updated_date')

    class Meta:
        model = User
        fields = ('id', 'username', 'mage_by_user', 'mage_last_updated',)

但是由于某些原因 'mage_last_updated' 字段没有出现！如果我删除 'mage_by_user' 然后它出错，抱怨 'mage_last_updated' 字段需要它存在。所以它在某个地方识别它。

我该如何解决这个问题？我该如何解决？

编辑：

这里是 json，为了这个问题（即，我插入了 mage 对象，以显示 updated_date 字段）json

{
    "id":1,
    "username":"admin",
    "mage_by_user":[{
        "id":3,
        "player":"admin",
        "name":"gandalf",
        "sub_race":"Foo",
        "faction":"Foo",
        "is_published":false,
        "updated_date":"2015-02-11T16:13:16.229890Z",
        "power_level":1,
        "energy_trait":7,
        "virtue":"prudence",
        "vice":"lust",
        "morality":7,
        "size":5,
        "arcana":{
            "Matter":0,
            "Death":0,
            "Fate":1,
            "Mind":0,
            "Prime":0,
            "Forces":0,
            "Spirit":0,
            "Time":0,
            "Space":0,
            "Life":0
        },            
        "mental_attributes":{
            "Wits":0,
            "Intelligence":1,
            "Resolve":0
        },
        "physical_attributes":{
            "Dexterity":0,
            "Stamina":0,
            "Strength":0
        },
        social_attributes":{
            "Composure":0,
            "Presence":0,
            "Manipulation":0
        },
        "mental_skills":{
            "Politics":0,
            "Academics":1,
            "Crafts":0,
            "Medicine":0,
            "Occult":0,
            "Science":0,
            "Investigation":0,
            "Computer":0
        },
        "physical_skills":{
            "Survival":0,
            "Athletics":0,
            "Weaponry":0,
            "Stealth":0,
            "Larceny":0,
            "Brawl":0,
            "Drive":0,
            "Firearms":0
        },
        "social_skills":{
            "Subterfuge":0,
            "Expression":0,
            "Socialize":0,
            "Streetwise":0,
            "Animal Ken":0,
            "Persuasion":0,
            "Empathy":0,
            "Intimidation":0
        }
    }]
}

此外，添加 many=True 对于只读字段 mage_last_updated 是不正确的，正如 Django 所抱怨的。这里mage_by_user是用户'owned'的法师列表

Answer 1

根据我们在 chat 中的讨论：

class UserSerializer(serializers.ModelSerializer):
    mage_by_user = serializers.PrimaryKeyRelatedField(
        many=True, queryset=Mage.objects.all())
    mage_last_updated = serializers.SerializerMethodField()

    class Meta:
        model = User
        fields = ('id', 'username', 'mage_by_user', 'mage_last_updated',)

    def get_mage_last_updated(self, obj):
        latest_mage = obj.mage_set.latest('updated_date')
        return latest_mage.updated_date

相关模型的只读字段没有出现，使用 Django Rest Framework？

Read only field from related model not appearing, with Django Rest Framework?

django

django-rest-framework

编辑：