Django序列化器get_or_create异常：Provider重复报错原因排查

背景代码 #

模型定义 #

class Article(AbstractBaseModel):
    manufacturer = models.ForeignKey(
        Manufacturer,
        on_delete=models.CASCADE,
        null=True,
        blank=True
    )

    provider1 = models.ForeignKey(
        Provider,
        on_delete=models.CASCADE,
        null=True,
        blank=True,
    )
    
    def get_absolute_url(self):
        return reverse(
            "smt_management_app:article-detail", kwargs={"name": self.name}
        )

class Manufacturer(models.Model):
    name = models.CharField(
        primary_key=True, max_length=50, null=False, blank=False
    )

    def get_absolute_url(self):
        return reverse(
            "smt_management_app:manufacturer-detail", kwargs={"name": self.name}
        )

class Provider(models.Model):
    name = models.CharField(
        primary_key=True, max_length=50, null=False, blank=False
    )

    def get_absolute_url(self):
        return reverse("smt_management_app:provider-detail", kwargs={"name": self.name})

序列化器与视图集 #

class ArticleSerializer(serializers.ModelSerializer):
    manufacturer = ManufacturerSerializer(required=False, allow_null=True)
    provider1 = ProviderSerializer(required=False, allow_null=True)

    class Meta:
        model = Article
        fields = [
            "name",
            "manufacturer",
            "provider1",
        ]

    def create(self, validated_data):
        manufacturer_data = validated_data.pop("manufacturer", None)
        if manufacturer_data:
            manufacturer, _ = Manufacturer.objects.get_or_create(
                name=manufacturer_data["name"]
            )
            validated_data["manufacturer"] = manufacturer

        provider1_data = validated_data.pop("provider1", None)
        if provider1_data:
            provider1, _= Provider.objects.get_or_create(
                name=provider1_data["name"]
            )
            validated_data["provider1"] = provider1

        article = Article.objects.create(**validated_data)
        return article

class ArticleViewSet(viewsets.ModelViewSet):
    queryset = Article.objects.all()
    serializer_class = ArticleSerializer
    filter_backends = (
        django_filters.rest_framework.DjangoFilterBackend,
        filters.SearchFilter,
        filters.OrderingFilter,
    )
    filterset_class = ArticleFilter
    ordering_fields = "__all__"

问题现象 #

提交POST请求创建新Article时，已知Manufacturer（name="123"）和Provider（name="abc"）均已存在，但仅Provider触发错误：
请求体：

{"name":"article1","manufacturer":{"name":"123"},"provider1":{"name":"abc"}}

错误信息：

{"provider1":{"name":["provider with this name already exists."]}}

原因分析 #

问题出在嵌套序列化器的验证阶段，而非create方法：

1. DRF的嵌套序列化器（如ProviderSerializer）默认行为是验证并创建新的关联对象。由于Provider的name是主键（自带唯一性约束），当提交已存在的name时，序列化器会触发唯一性验证，直接抛出错误，不会进入create方法中的get_or_create逻辑。
2. 你看到的"逻辑一致"只是ArticleSerializer中的代码，但ManufacturerSerializer和ProviderSerializer的实际定义存在差异——比如ManufacturerSerializer可能被设置了name字段只读、自定义了验证逻辑跳过唯一性检查，或是其他修改，导致它没有触发主键唯一性验证。

解决办法 #

你的业务意图是关联已存在的对象，不存在则自动创建，嵌套序列化器的默认行为不符合这个需求，建议改用SlugRelatedField：

方案1：直接关联已存在对象 #

如果只需要关联已存在的Manufacturer/Provider，不需要自动创建：

class ArticleSerializer(serializers.ModelSerializer):
    manufacturer = serializers.SlugRelatedField(
        queryset=Manufacturer.objects.all(),
        slug_field='name',
        required=False,
        allow_null=True
    )
    provider1 = serializers.SlugRelatedField(
        queryset=Provider.objects.all(),
        slug_field='name',
        required=False,
        allow_null=True
    )

    class Meta:
        model = Article
        fields = ["name", "manufacturer", "provider1"]

    def create(self, validated_data):
        article = Article.objects.create(**validated_data)
        return article

此时请求体可以简化为：

{"name":"article1","manufacturer":"123","provider1":"abc"}

方案2：自动创建不存在的对象 #

如果需要自动创建不存在的Manufacturer/Provider，可以自定义字段：

class CreateSlugRelatedField(serializers.SlugRelatedField):
    def to_internal_value(self, data):
        try:
            return self.get_queryset().get(**{self.slug_field: data})
        except self.queryset.model.DoesNotExist:
            return self.queryset.model.objects.create(**{self.slug_field: data})

class ArticleSerializer(serializers.ModelSerializer):
    manufacturer = CreateSlugRelatedField(
        queryset=Manufacturer.objects.all(),
        slug_field='name',
        required=False,
        allow_null=True
    )
    provider1 = CreateSlugRelatedField(
        queryset=Provider.objects.all(),
        slug_field='name',
        required=False,
        allow_null=True
    )

    class Meta:
        model = Article
        fields = ["name", "manufacturer", "provider1"]

内容的提问来源于stack exchange，提问作者Astrionn