如何爲DRF 3序列化程序創建附加的非模型CharField？

Question

這是我的串行：

class PostSerializer(serializers.ModelSerializer): 

    postType = serializers.CharField(default='posts'); 

    class Meta: 
     model = Post 
     fields = ('id', 'usersVoted', 'post', 'postType') 
     read_only_fields = ('id', 'owner', 'postType') 

postType是我要發送到前端用「帖子」的字符串值附加字段。我通過將它置於read_only_fields變量中來確保它是ReadOnly。問題是我收到一條錯誤消息：

AttributeError at /posts/ 
Got AttributeError when attempting to get a value for field `postType` on serializer `PostSerializer`. 
The serializer field might be named incorrectly and not match any attribute or key on the `Post` instance. 
Original exception text was: 'Post' object has no attribute 'postType'. 

有什麼辦法可以解決這個問題嗎？我不認爲SerializerMethodField是必要的，因爲我只是想將字符串'posts'添加到序列化程序中，因此不需要整個函數。

Answer 1

我相信你在DRF文檔答案：http://www.django-rest-framework.org/api-guide/fields/#serializermethodfield

SerializerMethodField這是一個只讀場...它可用於任何類型的數據添加到您的對象的序列化表示。

from django.contrib.auth.models import User 
from django.utils.timezone import now 
from rest_framework import serializers 

class UserSerializer(serializers.ModelSerializer): 
    days_since_joined = serializers.SerializerMethodField() 

    class Meta: 
     model = User 

    def get_days_since_joined(self, obj): 
     return (now() - obj.date_joined).days 

更新：現在對於你的情況：

class PostSerializer(serializers.ModelSerializer): 

    postType = serializers.SerializerMethodField() 

    class Meta: 
     model = Post 
     fields = ('id', 'usersVoted', 'post') 
     read_only_fields = ('id', 'owner') 

    def get_postType(): 
     return "posts" 

Answer 2

因爲read_only_fields應該是從模型而postType不是模型場你說的異常。