Django Rest框架不序列化SerializerMethodField

Question

我有两个模型：

from django.db import models

STATUSES = (
    ('f', 'Finished'),
)


class Battery(models.Model):
    energy = models.CharField(max_length=10)
    current = models.CharField(max_length=10)


class Charger(models.Model):
    status = models.CharField(max_length=1, choices=STATUSES)

我想创建序列化程序，将这两个模型序列化在一起。我的序列化程序.py：

from rest_framework import serializers
from .models import Battery, Charger


class BatterySerializer(serializers.ModelSerializer):
    class Meta:
        model = Battery


class ChargerSerializer(serializers.ModelSerializer):
    status = serializers.SerializerMethodField()

    class Meta:
        model = Charger

    def get_status(self, obj):
        return obj.get_status_display()


class DeviceSerializer(serializers.Serializer):
    battery = BatterySerializer()
    charger = ChargerSerializer()
    some_field = serializers.CharField()

因为充电器型号在状态字段中有选择，所以我添加SerializerMethodField以显示完整状态。然后我创建这样的视图：

class DeviceView(APIView):
    def get(self, request, format=None):
        battery = Battery.objects.get(id=1)
        charger = Charger.objects.get(id=1)
        battery_serializer = BatterySerializer(battery)
        charger_serializer = ChargerSerializer(charger)
        serializer = DeviceSerializer(data={
            'battery': battery_serializer.data,
            'charger': charger_serializer.data,
            'some_field': 'some_text'
        })
        if serializer.is_valid():
            return Response(serializer.validated_data)
        else:
            return Response(status = 500)

但是当我调用这个视图时，它返回带有空charger字段的json：

{
    "battery": {
        "energy": "12",
        "current": "34"
    },
    "charger": {},
    "some_field": "some_text"
}

但是当我创建一个只序列化充电器模型的视图时：

class ChargerView(APIView):
    def get(self, request, format=None):
        charger = Charger.objects.get(id=1)
        charger_serializer = ChargerSerializer(charger)
        return Response(charger_serializer.data)

它工作并返回此json：

{
    "id": 1,
    "status": "Finished"
}

为什么会这样？我错在哪里了？

Answer 1

查看Serializers的文档：

1. instance在有对象且必须序列化时传递。(link)
2. data在您已经序列化了数据并希望反序列化它并从中创建实例时传递。(link)
3. 当您有一个实例并且想要更新它时，instance和data都被传递

看看你的案例，我认为你不需要选项2和3，因为你有battery和charger实例，你需要一起序列化它。您不需要创建新实例，也不需要验证它，因此不需要将其作为data传递。

有两种方法可以做到这一点：

1.创建一个类Device，这样您就可以创建它的一个实例，然后使用DeviceSerializer序列化它：

class Device(object):

    def __init__(self, battery, charger, some_field):
        self.battery = battery
        self.charger = charger
        self.some_field  = some_field

class DeviceView(APIView):
    # then in the DeviceView you could create an instance and pass to the serializer
    def get(self, request, format=None):
        battery = Battery.objects.get(id=1)
        charger = Charger.objects.get(id=1)
        device = Device(battery=battery, charger=charger, some_field='some_text')
        serializer = DeviceSerializer(instance=device)
        return Response(serializer.data)

2.如果不想继续创建新类，可以直接创建一个dict，并将其作为实例传递：

class DeviceView(APIView):
    def get(self, request, format=None):
        battery = Battery.objects.get(id=1)
        charger = Charger.objects.get(id=1)
        # create a dict with required objects and pass it as instance of serializer
        device = {'battery': battery, 'charger': charger, 'some_field': 'some_text'}
        serializer = DeviceSerializer(instance=device)
        return Response(serializer.data)    

Answer 2

好像你在做你不必做的工作。如果在将充电器传递给DeviceSerializer之前对其进行序列化，则实际上传递的是dict，而不是Charger实例，dict没有get_status_display方法。您应该像这样直接传递Battery和Charger：

class DeviceView(APIView):
    def get(self, request, format=None):
        battery = Battery.objects.get(id=1)
        charger = Charger.objects.get(id=1)
        serializer = DeviceSerializer(instance={
            'battery': battery,
            'charger': charger,
            'some_field': 'some_text',
        })
        return Response(serializer.data)

请注意，还可以通过将SerializerMethodField替换为CharField来简化：

class ChargerSerializer(serializers.ModelSerializer):
    status = serializers.CharField(source='get_status_display')

    class Meta:
        model = Charger

编辑：正如AKS所指出的，当序列化（data用于反序列化）时，应该传递一个序列化程序instance，而不是data，并且不需要检查.is_valid()

Answer 3

在创建序列化程序实例时传递关键字数据，只有在反序列化数据时才使用此开关。 您应该创建一个带有所需字段的对象的DeviceSerializer。 我没试过，但可能是这样的

class Device(object):
    def __init__(self, battery, charger, name, ):
        self.battery = battery
        self.charger = charger
        self.some_field = name

class DeviceView(APIView):
    def get(self, request, format=None):

        d=Device(Battery.objects.get(id=1),Charger.objects.get(id=1),"somename")
        serializer = DeviceSerializer(d)
            return Response(serializer.data)