传递给我的ListSerializer的to_representation函数的“实例”是什么？

Question

这个项目的目标是创建一个API，每小时刷新与最新的投注赔率的游戏，我将从互联网上抓取每小时。返回的JSON的目标结构将是每个游戏作为父对象，嵌套子对象将是更新日期之前抓取的每个date的前1个记录。我的理解是，实现这一点的最好方法是修改ListSerializer中的to_representation函数以返回适当的查询集。

因为我需要父元素的game_id来获取相应游戏的子元素，所以我尝试从传递的数据中提取game_id。问题是，当我通过异常看到该行包含的内容时，它看起来是正确填充的，但当我让完整代码运行时，我得到了一个列表索引超出范围的异常。

对于ex。

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raise异常，我得到的列表索引超出了范围。我最初的想法是，还有一些东西依赖于以列表形式返回的“数据”，所以我创建了列表理解片段，但这并不能解决问题。

所以，我的问题是: 1)有没有更简单的方法来完成我要做的事情？我没有使用postgres后端，所以我不能使用截然不同的。2)如果不是，我不清楚传入的是什么实例，也不清楚预计会返回什么。我查阅了文档，它看起来需要一个字典，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

我很感谢任何提前了解这里发生的事情的帮助。

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

要回答标题中的问题：

传递给Serializer.to_representation()的instance是初始化序列化程序时传递的实例

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

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

通常，您不必从ListSerializer本身继承。你可以从BaseSerializer继承，只要你在初始化时传递many=True，它就会自动‘变成aListSerializer`。You can see this in action here

来回答你的问题

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)