传递给 ListSerializer 的 to_representation 函数的 "instance" 是什么？

Question

这个项目的目标是创建一个 API 每小时刷新一次的游戏列表的最新投注赔率，我将每小时从互联网上收集这些游戏。 JSON returned 的目标结构将每个游戏作为父对象，嵌套的子对象将是每个 linemakers 在更新日期前被抓取的前 1 条记录。我的理解是，实现此目的的最佳方法是将 ListSerializer 中的 to_representation 函数修改为 return 适当的查询集。

因为我需要父元素的 game_id 来获取相应游戏的子元素，所以我试图从传递的数据中提取 game_id。问题是当我通过异常看到它包含的内容时，该行看起来被正确填充，但是当我让完整代码运行时，我得到一个列表索引超出范围异常。

例如

class OddsMakerListSerializer(serializers.ListSerializer):
    def to_representation(self, data):
        game = data.all()[0].game_id

        #if I put this here it evaluates to 1 which should run the raw sql below correctly
        raise Exception(game) 
        data = OddsMaker.objects.filter(odds_id__in = RawSQL(''' SELECT o.odds_id
                                                                    FROM gamesbackend_oddsmaker o
                                                              INNER JOIN (
                                                                          SELECT game_id
                                                                               , oddsmaker
                                                                               , max(updated_datetime)            as last_updated
                                                                            FROM gamesbackend_oddsmaker
                                                                           WHERE game_id = %s
                                                                        GROUP BY game_id
                                                                               , oddsmaker
                                                                         ) l on o.game_id = l.game_id
                                                                            and o.oddsmaker = l.oddsmaker
                                                                            and o.updated_datetime = l.last_updated
                                                              ''', [game]))
        #if I put this here the data appears to be populated correctly and contain the right data
        raise Exception(data)
        data = [game for game in data]
        return data

现在，如果我删除这些引发的异常，我会得到列表索引超出范围。我最初的想法是，还有其他一些东西依赖于 "data" 被 returned 作为列表，所以我创建了列表理解片段，但这并没有解决问题。

所以，我的问题是 1) 是否有更简单的方法来完成我的目标？我没有使用 postgres 后端，所以 distinct on 对我不可用。和 2) 如果不是，我不清楚传入的实例是什么，或者预期 returned 是什么。我查阅了文档，它看起来好像需要一本字典，这可能是问题的一部分，但错误消息再次引用了一个列表。 https://www.django-rest-framework.org/api-guide/serializers/#overriding-serialization-and-deserialization-behavior

感谢任何帮助我提前了解这里发生的事情的人。

编辑：其余的序列化程序：

class OddsMakerSerializer(serializers.ModelSerializer):
    class Meta:
        list_serializer_class = OddsMakerListSerializer
        model = OddsMaker
        fields = ('odds_id','game_id','oddsmaker','home_ml',
                  'away_ml','home_spread','home_spread_odds',
                  'away_spread_odds','total','total_over_odds',
                  'total_under_odds','updated_datetime')


class GameSerializer(serializers.ModelSerializer):
    oddsmaker_set = OddsMakerSerializer(many=True, read_only=True)

    class Meta:
        model = Game
        fields = ('game_id','date','sport', 'home_team',
                  'away_team','home_score', 'away_score',
                  'home_win','away_win', 'game_completed',
                  'oddsmaker_set')

models.py:

class Game(models.Model):
    game_id = models.AutoField(primary_key=True)
    date = models.DateTimeField(null=True)
    sport=models.CharField(max_length=256, null=True)
    home_team = models.CharField(max_length=256, null=True)
    away_team = models.CharField(max_length=256, null=True)
    home_score = models.IntegerField(default=0, null=True)
    away_score = models.IntegerField(default=0, null=True)
    home_win = models.BooleanField(default=0, null=True)
    away_win = models.BooleanField(default=0, null=True)
    game_completed = models.BooleanField(default=0, null=True)

class OddsMaker(models.Model):
    odds_id = models.AutoField(primary_key=True)
    game = models.ForeignKey('Game', on_delete = models.CASCADE)
    oddsmaker = models.CharField(max_length=256)
    home_ml = models.IntegerField(default=999999)
    away_ml = models.IntegerField(default=999999)
    home_spread = models.FloatField(default=999)
    home_spread_odds = models.IntegerField(default=9999)
    away_spread_odds = models.IntegerField(default=9999)
    total = models.FloatField(default=999)
    total_over_odds = models.IntegerField(default=999)
    total_under_odds = models.IntegerField(default=999)
    updated_datetime = models.DateTimeField(auto_now=True)

views.py:

class GameView(viewsets.ModelViewSet):      
  queryset = Game.objects.all()             
  serializer_class = GameSerializer

谢谢

Answer 1

回答标题中的问题：

传递给Serializer.to_representation()的instance就是你在初始化序列化器时传递的实例

queryset = MyModel.objects.all()
Serializer(queryset, many=True)

instance = MyModel.objects.all().first()
Serializer(data)

通常您不必继承 ListSerializer 本身。您可以从 BaseSerializer 继承，每当您在初始化期间传递 many=True 时，它将自动“成为 aListSerializer”。 You can see this in action here

回答你的问题

from django.db.models import Max
class OddsMakerListSerializer(serializers.ListSerializer):
    def to_representation(self, data): # data passed is a queryset of oddsmaker                 
        # Do your filtering here
        latest_date = data.aggregate(
            latest_date=Max('updated_datetime')
        ).get('latest_date').date()   
        latest_records = data.filter(
            updated_date_time__year=latest_date.year,
            updated_date_time__month=latest_date.month,
            updated_date_time__day=latest_date.day
        )
        return super().to_representation(latest_records)

传递给 ListSerializer 的 to_representation 函数的 "instance" 是什么？

What is the "instance" being passed to the to_representation function of my ListSerializer?

python

django

django-serializer

django-rest-framework

回答标题中的问题：

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