django - 使用 Django Rest Framework 3.2.2 与现有对象的可写嵌套序列化器

Question

考虑一个具有关联类别的列表模型。我想通过使用数据进行 POST 来为现有类别创建一个新列表:{"title": "myapp", "category": {"name": "Business"}}，其中 title 是应创建的列表的标题，Business 是用于此新列表的现有类别的名称。

当我尝试发出此类请求并为此实例化 ListingSerializer 时，我收到一条错误，指示类别名称必须是唯一的 - 我不想创建新类别，但是使用现有的代替。我尝试将类别字段上的验证器设置为 []，但这并没有改变行为。

我可以使用 SlugRelatedField，但这会迫使我的请求数据看起来更像 {"title": "myapp", "category": "Business"} ，这不是我想要的。我尝试使用 SlugRelatedField 的 source 参数来指定嵌套关系，但这也不起作用:

category = serializers.SlugRelatedField(
        slug_field='category.name',
        queryset=models.Category.objects.all()
    )

产量:

  "category": [
    "Object with name={'name': 'Business'} does not exist."
  ]

模型.py:

import django.contrib.auth
from django.db import models
from django.conf import settings

class Profile(models.Model):
    display_name = models.CharField(max_length=255)
    user = models.OneToOneField(settings.AUTH_USER_MODEL)

class Category(models.Model):
    name = models.CharField(max_length=50, unique=True)
    description = models.CharField(max_length=200)

class Listing(models.Model):
    title = models.CharField(max_length=50, unique=True)
    category = models.ForeignKey(Category, related_name='listings', null=True)
    owners = models.ManyToManyField(
        Profile,
        related_name='owned_listings',
        db_table='profile_listing',
        blank=True
    )

序列化器.py:

import logging
import django.contrib.auth
from rest_framework import serializers
import myapp.models as models

logger = logging.getLogger('mylogger')

class ShortUserSerializer(serializers.ModelSerializer):
    class Meta:
        model = django.contrib.auth.models.User
        fields = ('username', 'email')

class ProfileSerializer(serializers.ModelSerializer):
    user = ShortUserSerializer()
    class Meta:
        model = models.Profile
        fields = ('user', 'display_name')
        read_only = ('display_name',)

class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = models.Category
        fields = ('name', 'description')
        read_only = ('description',)


class ListingSerializer(serializers.ModelSerializer):
    owners = ProfileSerializer(required=False, many=True)
    # TODO: how to indicate that this should look for an existing category?
    category = CategorySerializer(required=False, validators=[])

    class Meta:
        model = models.Listing
        depth = 2

    def validate(self, data):
        logger.info('inside ListingSerializer validate')
        return data

    def create(self, validated_data):
        logger.info('inside ListingSerializer.create')
        # not even getting this far...

views.py:

import logging

from django.http import HttpResponse
from django.shortcuts import get_object_or_404

import django.contrib.auth

from rest_framework import viewsets
from rest_framework.response import Response

import myapp.serializers as serializers
import myapp.models as models


# Get an instance of a logger
logger = logging.getLogger('mylogger')

class CategoryViewSet(viewsets.ModelViewSet):
    queryset = models.Category.objects.all()
    serializer_class = serializers.CategorySerializer

class UserViewSet(viewsets.ModelViewSet):
    queryset = django.contrib.auth.models.User.objects.all()
    serializer_class = serializers.ShortUserSerializer

class ProfileViewSet(viewsets.ModelViewSet):
    queryset = models.Profile.objects.all()
    serializer_class = serializers.ProfileSerializer

class ListingViewSet(viewsets.ModelViewSet):
    logger.info('inside ListingSerializerViewSet')
    queryset = models.Listing.objects.all()
    serializer_class = serializers.ListingSerializer

完整示例:https://github.com/arw180/drf-example

Answer 1

这并不理想，但我确实找到了解决我的问题的解决方案(我正在等待接受它作为答案，希望其他人可以做得更好)。有两部分:

首先，使用partial=True初始化 ListingSerializer 时的参数(http://www.django-rest-framework.org/api-guide/serializers/#partial-updates)。然后使用序列化器的validate方法获取与输入数据对应的实际模型实例。

其次，显式删除 name 的验证器CategorySerializer 中的字段。这尤其糟糕，因为它不仅仅影响 ListingSerializer 。

遗漏任何一部分都会导致在实例化序列化器时引发验证错误。

对views.py的修改:

class ListingViewSet(viewsets.ModelViewSet):
    queryset = models.Listing.objects.all()
    serializer_class = serializers.ListingSerializer

    def create(self, request):
        serializer = serializers.ListingSerializer(data=request.data,
            context={'request': request}, partial=True)
        if not serializer.is_valid():
            logger.error('%s' % serializer.errors)
            return Response(serializer.errors,
                  status=status.HTTP_400_BAD_REQUEST)

        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)

对serializers.py的修改:

class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = models.Category
        fields = ('name', 'description')
        read_only = ('description',)
        # also need to explicitly remove validators for `name` field
        extra_kwargs = {
            'name': {
                'validators': []
            }
        }

class ListingSerializer(serializers.ModelSerializer):
    owners = ProfileSerializer(required=False, many=True)
    category = CategorySerializer(required=False)
    class Meta:
        model = models.Listing
        depth = 2

    def validate(self, data):
        # manually get the Category instance from the input data
        data['category'] = models.Category.objects.get(name=data['category']['name'])
        return data

    def create(self, validated_data):
        title = validated_data['title']

        listing = models.Listing(title=validated_data['title'],
            category=validated_data['category'])

        listing.save()

        if 'owners' in validated_data:
            logger.debug('owners: %s' % validated_data['owners'])
            for owner in validated_data['owners']:
                print ('adding owner: %s' % owner)
                listing.owners.add(owner)
        return listing

我会稍等一下接受这个答案，以防有人能提出更好的解决方案(例如如何使 source 参数与 SlugRelatedField 一起正常工作) - 我有一个使用的工作示例上面的解决方案位于 https://github.com/arw180/drf-example如果你想尝试。我也很想听到关于为什么 extra_kwargs 的评论CategorySerializer 中的东西是必要的- 为什么不像这样实例化它:category = CategorySerializer(required=False, validators=[])足够(在 ListingSerializer 中)？更新:我相信这不起作用，因为唯一的验证器是从数据库约束中自动添加的，并且无论此处设置的任何显式验证器如何运行，如本答案中所述:http://iswwwup.com/t/3bf20dfabe1f/python-order-of-serializer-validation-in-django-rest-framework.html