Django DRF嵌套序列化器无法保存模型：求问题排查与解决

问题概述 #

使用Django DRF嵌套序列化器时出现保存失败，报错信息：NOT NULL constraint failed: VideoMaker_videomaker.duration_id，无法完成模型数据持久化。相关代码、错误信息及期望返回结果如下：

模型代码 #

class Duration(models.Model):
    start_time = models.PositiveIntegerField(blank=True,null=True)
    end_time = models.PositiveIntegerField(blank=True,null=True)

    def __str__(self):
        self.end_time


class VideoMaker(models.Model):
    CHOICE_SELECT = [
        ('vo','voice over'),
        ('bg_music','backgournd music'),
        ('video_music','vidio music'),
    ]
    typee = models.CharField(max_length=15,choices=CHOICE_SELECT)
    high_volume = models.PositiveIntegerField()
    low_volume = models.PositiveIntegerField()
    video_component_id = models.CharField(max_length=300,null=True,blank=True)
    url = models.URLField(blank=True,null=True)
    duration = models.ForeignKey(Duration, on_delete=models.CASCADE)

    def __str__(self):
        return self.id

序列化器代码 #

class DuratinSeriaizer(serializers.ModelSerializer):
    class Meta:
        model = Duration
        fields = [
            'id',
            'start_time',
            'end_time',
        ]


class VideoMakerSerializer(serializers.ModelSerializer):
    duration = DuratinSeriaizer()
    class Meta:
        model = VideoMaker
        fields = [
            'id',
            'typee',
            'high_volume',
            'low_volume',
            'video_component_id',
            'url',
            'duration',
        ]

    def create(self, validated_data):
        datas = validated_data.pop('duration')
        duration_data = VideoMaker.objects.create(**validated_data)
        for datas in datas:
            Duration.objects.create(duration=duration_data,**datas)
        Duration.save()
        return duration_data

视图代码 #

class AudioCreateApiView(generics.ListCreateAPIView):
    queryset = VideoMaker.objects.all()
    serializer_class = VideoMakerSerializer

期望返回结果 #

{
    "id": 6,
    "typee": "vo",
    "high_volume": 65,
    "low_volume": 123,
    "video_component_id": "wertyuio",
    "url": "",
    "duration": {
        "id": 9,
        "start_time": 21,
        "end_time": 98
    }
}

问题根源 #

1. 外键依赖逻辑颠倒：VideoMaker的duration是必填外键，原代码先创建VideoMaker实例，此时未关联任何Duration，触发NOT NULL约束错误。
2. 代码逻辑错误：
   • 错误将duration的单条字典数据当成列表循环处理
   • 错误调用类方法Duration.save()，应该操作实例的save()方法
   • 关联字段名称错误：Duration模型不存在duration字段，无需反向关联

修正方案 #

1. 修正模型代码（修复__str__方法的语法问题） #

class Duration(models.Model):
    start_time = models.PositiveIntegerField(blank=True, null=True)
    end_time = models.PositiveIntegerField(blank=True, null=True)

    def __str__(self):
        return str(self.end_time)  # 补充return并转为字符串类型


class VideoMaker(models.Model):
    CHOICE_SELECT = [
        ('vo', 'voice over'),
        ('bg_music', 'backgournd music'),
        ('video_music', 'vidio music'),
    ]
    typee = models.CharField(max_length=15, choices=CHOICE_SELECT)
    high_volume = models.PositiveIntegerField()
    low_volume = models.PositiveIntegerField()
    video_component_id = models.CharField(max_length=300, null=True, blank=True)
    url = models.URLField(blank=True, null=True)
    duration = models.ForeignKey(Duration, on_delete=models.CASCADE)

    def __str__(self):
        return str(self.id)  # 整数转字符串，符合__str__返回要求

2. 核心修正序列化器代码（调整创建顺序） #

class DurationSerializer(serializers.ModelSerializer):  # 修正拼写错误DuratinSeriaizer
    class Meta:
        model = Duration
        fields = ['id', 'start_time', 'end_time']


class VideoMakerSerializer(serializers.ModelSerializer):
    duration = DurationSerializer()

    class Meta:
        model = VideoMaker
        fields = ['id', 'typee', 'high_volume', 'low_volume', 'video_component_id', 'url', 'duration']

    def create(self, validated_data):
        # 先取出嵌套的duration数据
        duration_data = validated_data.pop('duration')
        # 先创建Duration实例
        duration_instance = Duration.objects.create(**duration_data)
        # 创建VideoMaker时关联已生成的Duration实例
        videomaker_instance = VideoMaker.objects.create(duration=duration_instance, **validated_data)
        return videomaker_instance

3. 视图代码无需修改 #

保持原AudioCreateApiView代码即可。

验证效果 #

发送如下请求体：

{
    "typee": "vo",
    "high_volume": 65,
    "low_volume": 123,
    "video_component_id": "wertyuio",
    "url": "",
    "duration": {
        "start_time": 21,
        "end_time": 98
    }
}

接口将返回符合期望的嵌套结构数据，且数据成功写入数据库。

内容的提问来源于stack exchange，提问作者M. Roshan