覆盖 Django (DRF) 序列化程序对象 GET

Question

我正在尝试将一些 raw sql“注入”到我的 DRF 嵌套序列化程序中：

# SERIALIZERS

class CarSerializer(serializers.ModelSerializer):

    class Meta:
        model = Car
        fields = '__all__'

class DriverSerializer(serializers.ModelSerializer):
    car = CarSerializer()   # <--- here I don't want to get the Car object but rather inject a raw sql.

    class Meta:
        model = Driver
        fields = '__all__'

由于我使用的是 MariaDB 版本控制表，因此需要 SQL 注入来请求特定版本的数据，但这无关紧要。如何覆盖从CarSerializer 获取对象的方法？谢谢。

Answer 1

这是未经测试的，但我认为您想覆盖 DriverSerializer 中的 __init__，然后通过 data 加载原始 SQL 的结果，如下所示：

class DriverSerializer(serializers.ModelSerializer):
     [...]
     def __init__(self, *args, **kwargs):
          super(DriverSerializer, self).__init__(*args, **kwargs)
          name_map = {'column_1': 'obj_attr_1', 'column_2': 'obj_attr_1', 'pk': 'id'}
          raw = Car.objects.raw('SELECT ... FROM ...', translations=name_map)
          data = {k: getattr(raw[0], k) for k in name_map.keys()}
          self.car = CarSerializer(data=data)

Answer 2

你可以在你的模型下定义方法来获取相关的 Car

class Car(models.Model):

    def current_car(self):
        return Car.objects.raw('SELECT ... FROM ...')[0]

然后在序列化器中你可以重用下面的方法

class DriverSerializer(serializers.ModelSerializer):
    car = CarSerializer(source="current_car")

    class Meta:
        model = Driver
        fields = (...)

Answer 3

感谢大家的回答，尽管我的解决方案不如@yvesonline 和@iklinak 建议的那样干净，但我设法使它工作：

我首先查看了关于覆盖序列化程序的官方 DRF 文档：https://www.django-rest-framework.org/api-guide/serializers/#overriding-serialization-and-deserialization-behavior

我特别感兴趣的是方法的覆盖：.to_representation(self, instance)，它控制从数据库中获取对象：

from datetime import datetime as dt
from collections import OrderedDict
from rest_framework.relations import PKOnlyObject
from rest_framework.fields import SkipField, empty

    def __init__(
            self, instance=None, data=empty, asTime=str(dt.now()), **kwargs):
        self.asTime = asTime
        self.instance = instance
        if data is not empty:
            self.initial_data = data
        self.partial = kwargs.pop('partial', False)
        self._context = kwargs.pop('context', {})
        kwargs.pop('many', None)
        super().__init__(**kwargs)

    def to_representation(self, instance):
        # substitute instance with my raw query
        # WARNING: self.asTime is a custom variable, check the
        # __init__ method above!

        instance = Car.objects.raw(
            '''
                    select * from db_car
                    for system_time as of timestamp %s
                    where id=%s;
                ''', [self.asTime, instance.id])[0]

        ret = OrderedDict()
        fields = self._readable_fields

        for field in fields:
            try:
                attribute = field.get_attribute(instance)
            except SkipField:
                continue

            check_for_none = attribute.pk if isinstance(
                attribute, PKOnlyObject) else attribute
            if check_for_none is None:
                ret[field.field_name] = None
            else:
                ret[field.field_name] = field.to_representation(attribute)

        return ret

您可以在这里找到原始代码：https://github.com/encode/django-rest-framework/blob/19655edbf782aa1fbdd7f8cd56ff9e0b7786ad3c/rest_framework/serializers.py#L335

然后终于在DriverSerializer类中：

class DriverSerializer(serializers.ModelSerializer):
    car = CarSerializer(asTime='2021-02-05 14:34:00')

    class Meta:
        model = Driver
        fields = '__all__'