ContentType 對象的 django-rest-framework 序列化程序

Question

我正在構建一個活動模型，有點類似於這個包。 它有一個演員、動詞和目標。

class Activity(models.Model):
    actor_type = models.ForeignKey(ContentType, related_name='actor_type_activities')
    actor_id = models.PositiveIntegerField()
    actor = GenericForeignKey('actor_type', 'actor_id')
    verb = models.CharField(max_length=10)
    target_type = models.ForeignKey(ContentType, related_name='target_type_activities')
    target_id = models.PositiveIntegerField()
    target = GenericForeignKey('target_type', 'target_id')
    pub_date = models.DateTimeField(default=timezone.now)

現在，無論何時創建任何模型（Tender、Job 和 News）的新對象，都會創建一個新的 Activity 對象， target是這三個模型中任何一個的對象。

例如。 用戶（演員）發布（動詞）標題（目標）

class Tender(models.Model):
    title = models.CharField(max_length=256)
    description = models.TextField()

class Job(models.Model):
    title = models.CharField(max_length=256)
    qualification = models.CharField(max_length=256)

class News(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL)
    title = models.CharField(max_length=150)

為了獲得這些數據，我正在制作一個 API，它將為我提供所需的 json 數據。 我正在為此使用django-rest-framework並且非常新。

class ActorSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = User
        fields = ('id', 'username', 'email')

class ActivitySerializer(serializers.HyperlinkedModelSerializer):
    actor = ActorSerializer()
    class Meta:
        model = Activity
        fields = ('url', 'actor', 'verb', 'pub_date')

在上面的序列化程序中，我知道actor將是 User。 所以我將 User 模型用於ActorSerializer類。 但是對於target ，它可以是這三種模型中的任何一種（News/Job/Tender）。

如何為 ContentType 對象創建序列化程序（例如TargetSerialier類），以便我可以在ActivitySerializer類字段中使用target ？

Answer 1

好的，所以在這里回答我自己的問題。 我對 zymud 的回答有一些幫助。 因此，顯然在文檔中，有一種方法可以序列化通用關系。

所以，我所要做的就是創建一個自定義字段並將該字段關聯到序列化程序本身：

class ActivityObjectRelatedField(serializers.RelatedField):
    def to_representation(self, value):
        if isinstance(value, User):
            return 'User: ' + value.username
        elif isinstance(value, News):
            return 'News: ' + value.title
        elif isinstance(value, Job):
            return 'Job: ' + value.title
        elif isinstance(value, Tender):
            return 'Tender: ' + value.title
        raise Exception('Unexpected type of tagged object')


class ActivitySerializer(serializers.HyperlinkedModelSerializer):
    actor = ActivityObjectRelatedField(read_only=True)
    target = ActivityObjectRelatedField(read_only=True)

    class Meta:
        model = Activity
        fields = ('url', 'actor', 'verb', 'target', 'pub_date')

Answer 2

您可以為通用鍵實現自定義字段。 示例：

from django.core.urlresolvers import resolve
from rest_framework.fields import Field

class GenericRelatedField(Field):
    """
    A custom field that expect object URL as input and transforms it
    to django model instance.
    """
    read_only = False
    _default_view_name = '%(model_name)s-detail'
    lookup_field = 'pk'

    def __init__(self, related_models=(), **kwargs):
        super(GenericRelatedField, self).__init__(**kwargs)
        # related models - list of models that should be acceptable by 
        # field. Note that all this models should have corresponding 
        # endpoint.
        self.related_models = related_models

    def _get_url_basename(self, obj):
        """ Get object URL basename """
        format_kwargs = {
            'app_label': obj._meta.app_label,
            'model_name': obj._meta.object_name.lower()
        }
        return self._default_view_name % format_kwargs

    def _get_request(self):
        try:
            return self.context['request']
        except KeyError:
            raise AttributeError('GenericRelatedField have to be initialized with `request` in context')

    def to_representation(self, obj):
        """ Serializes any object to its URL representation """
        kwargs = {self.lookup_field: getattr(obj, self.lookup_field)}
        request = self._get_request()
        return request.build_absolute_uri(reverse(self._get_url_basename(obj), kwargs=kwargs))

    def clear_url(self, url):
        """ Removes domain and protocol from url """
        if url.startswith('http'):
             return '/' + url.split('/', 3)[-1]
        return url

    def get_model_from_resolve_match(self, match):
        queryset = match.func.cls.queryset
        if queryset is not None:
            return queryset.model
        else:
            return match.func.cls.model

    def instance_from_url(self, url):
        url = self.clear_url(url)
        match = resolve(url)
        model = self.get_model_from_resolve_match(match)
        return model.objects.get(**match.kwargs)


    def to_internal_value(self, data):
        """ Restores model instance from its URL """
        if not data:
            return None
        request = self._get_request()
        user = request.user
        try:
            obj = self.instance_from_url(data)
            model = obj.__class__
        except (Resolver404, AttributeError, MultipleObjectsReturned, ObjectDoesNotExist):
            raise serializers.ValidationError("Can`t restore object from url: %s" % data)
        if model not in self.related_models:
            raise serializers.ValidationError('%s object does not support such relationship' % str(obj))
        return obj

用法示例：

class ActivitySerializer(serializers.HyperlinkedModelSerializer):
    target = GenericRelatedField(related_models=(News, Job, Tender))
    ...

Answer 3

根據文檔，有一個第三方庫已經完成了繁重的工作：

https://www.django-rest-framework.org/api-guide/relations/#rest-framework-generic-relations

實際上它非常整潔，我的序列化器類最終只有幾行可讀的行：

class ActivityTypeSerializer(serializers.ModelSerializer):
    target = GenericRelatedField({
        User: UserSerializer(),
        Device: DeviceSerializer(),
    })

    class Meta:
        model = Activity
        fields = ('target', 'target_id', 'verb', 'target_ct',)