Django REST框架：为嵌套序列化程序设置预取

我的Django驱动的带有DRFAPI的应用程序运行良好，但随着数据库中填充了实际数据，我开始遇到性能问题。我使用Django调试工具栏进行了一些评测，发现我的许多端点在返回数据的过程中会发出数十到数百个查询

我预料到了这一点，因为我以前没有对数据库查询进行过任何优化。但是，现在我正在设置预取，当序列化程序嵌套在不同的序列化程序中时，我很难使用正确预取的序列化程序数据。我一直在用它来指导如何思考不同的预取方法

目前，当我点击

/api/readinggroups/

端点时，我的

ReadingGroup

序列化程序确实正确预取了数据。我的问题是

/api/userbookstats/

端点，它返回所有

userbookstats

对象。相关的序列化程序，

UserBookStatsSerializer

，具有嵌套的

ReadingGroupSerializer

模型、序列化器和视图集如下所示：

型号.py

class ReadingGroup(models.model):
    owner = models.ForeignKeyField(settings.AUTH_USER_MODEL)
    users = models.ManyToManyField(settings.AUTH_USER_MODEL)
    book_type = models.ForeignKeyField(BookType)
    ....
    <other group related fields>

   def __str__(self):
     return '%s group: %s' % (self.name, self.book_type)

class UserBookStats(models.Model):
    reading_group = models.ForeignKey(ReadingGroup)
    user = models.ForeignKey(settings.AUTH_USER_MODEL)
    alias = models.CharField()

    total_books_read = models.IntegerField(default=0)
    num_books_owned = models.IntegerField(default=0)
    fastest_read_time = models.IntegerField(default=0)
    average_read_time = models.IntegerField(default=0)

class ReadingGroupSerializer(serializers.ModelSerializer):
    users = UserSerializer(many = True,read_only=True)
    owner = UserSerializer(read_only=True)

    class Meta:
      model = ReadingGroup
      fields = ('url', 'id','owner', 'users')

    @staticmethod
    def setup_eager_loading(queryset):
      #select_related for 'to-one' relationships
      queryset = queryset.select_related('owner')

      #prefetch_related for 'to-many' relationships
      queryset = queryset.prefetch_related('users')

      return queryset

class UserBookStatsSerializer(serializers.HyperlinkedModelSerializer):
    reading_group = ReadingGroupSerializer()
    user = UserSerializer()
    awards = AwardSerializer(source='award_set', many=True)

    class Meta:
      model = UserBookStats
      fields = ('url', 'id', 'alias', 'total_books_read', 'num_books_owned', 
              'average_read_time', 'fastest_read_time', 'awards')

    @staticmethod
    def setup_eager_loading(queryset):
      #select_related for 'to-one' relationships
      queryset = queryset.select_related('user')

      #prefetch_related for 'to-many' relationships
      queryset = queryset.prefetch_related('awards_set')

      #setup prefetching for nested serializers
      groups = Prefetch('reading_group', queryset ReadingGroup.objects.prefetch_related('userbookstats_set'))        
      queryset = queryset.prefetch_related(groups)

      return queryset

class ReadingGroupViewset(views.ModelViewset):

  def get_queryset(self):
    qs = ReadingGroup.objects.all()
    qs = self.get_serializer_class().setup_eager_loading(qs)
    return qs

class UserBookStatsViewset(views.ModelViewset):

  def get_queryset(self):
    qs = UserBookStats.objects.all()
    qs = self.get_serializer_class().setup_eager_loading(qs)
    return qs

视图.py

class ReadingGroup(models.model):
    owner = models.ForeignKeyField(settings.AUTH_USER_MODEL)
    users = models.ManyToManyField(settings.AUTH_USER_MODEL)
    book_type = models.ForeignKeyField(BookType)
    ....
    <other group related fields>

   def __str__(self):
     return '%s group: %s' % (self.name, self.book_type)

class UserBookStats(models.Model):
    reading_group = models.ForeignKey(ReadingGroup)
    user = models.ForeignKey(settings.AUTH_USER_MODEL)
    alias = models.CharField()

    total_books_read = models.IntegerField(default=0)
    num_books_owned = models.IntegerField(default=0)
    fastest_read_time = models.IntegerField(default=0)
    average_read_time = models.IntegerField(default=0)

class ReadingGroupSerializer(serializers.ModelSerializer):
    users = UserSerializer(many = True,read_only=True)
    owner = UserSerializer(read_only=True)

    class Meta:
      model = ReadingGroup
      fields = ('url', 'id','owner', 'users')

    @staticmethod
    def setup_eager_loading(queryset):
      #select_related for 'to-one' relationships
      queryset = queryset.select_related('owner')

      #prefetch_related for 'to-many' relationships
      queryset = queryset.prefetch_related('users')

      return queryset

class UserBookStatsSerializer(serializers.HyperlinkedModelSerializer):
    reading_group = ReadingGroupSerializer()
    user = UserSerializer()
    awards = AwardSerializer(source='award_set', many=True)

    class Meta:
      model = UserBookStats
      fields = ('url', 'id', 'alias', 'total_books_read', 'num_books_owned', 
              'average_read_time', 'fastest_read_time', 'awards')

    @staticmethod
    def setup_eager_loading(queryset):
      #select_related for 'to-one' relationships
      queryset = queryset.select_related('user')

      #prefetch_related for 'to-many' relationships
      queryset = queryset.prefetch_related('awards_set')

      #setup prefetching for nested serializers
      groups = Prefetch('reading_group', queryset ReadingGroup.objects.prefetch_related('userbookstats_set'))        
      queryset = queryset.prefetch_related(groups)

      return queryset

class ReadingGroupViewset(views.ModelViewset):

  def get_queryset(self):
    qs = ReadingGroup.objects.all()
    qs = self.get_serializer_class().setup_eager_loading(qs)
    return qs

class UserBookStatsViewset(views.ModelViewset):

  def get_queryset(self):
    qs = UserBookStats.objects.all()
    qs = self.get_serializer_class().setup_eager_loading(qs)
    return qs

我已经优化了

ReadingGroup

端点的预取（实际上我发布了关于消除该端点重复查询的内容），现在我正在研究

UserBookStats

端点

我遇到的问题是，在

UserBookStatsSerializer

中当前的

设置\u eager\u加载

时，它似乎没有使用由

ReadingGroupSerializer

中的eager加载方法设置的预取。我对

预回迁

对象的语法仍然有点模糊，我是受了这个优秀答案的启发而尝试这种方法的

显然，

UserBookStatsViewset

的

get\u queryset

方法没有为

ReadingGroup

对象调用

setup\u eager\u loading

，但是我确信有一种方法可以完成相同的预取。

prefetch\u related（）

支持使用双下划线语法预取内部关系：

queryset = queryset.prefetch_related('reading_group', 'reading_group__users', 'reading_group__owner') 

---

我不认为Django REST为自动获取所有必需字段提供了任何现成的解决方案。

手动预取所有嵌套关系的替代方案，还有一个名为的包，它将自动遍历模型和序列化程序上的相关字段，以查找所有需要在

prefetch\u related

和

select\u related

调用中提及的模型。您只需将

AutoPrefetchViewSetMixin

添加到您的视图集中：

from django_auto_prefetching import AutoPrefetchViewSetMixin

class ReadingGroupViewset(AutoPrefetchViewSetMixin, views.ModelViewset):

  def get_queryset(self):
    qs = ReadingGroup.objects.all()
    return qs

class UserBookStatsViewset(AutoPrefetchViewSetMixin, views.ModelViewset):

  def get_queryset(self):
    qs = UserBookStats.objects.all()
    return qs

---

任何具有更复杂的

Prefetch

对象的额外预取都可以添加到视图集中的

get\u queryset

方法中。

您是在询问优雅的解决方案还是其他解决方案

queryset=queryset.prefetch\u related（'reading\u group'、'reading\u group\u users'、'reading\u group\u owner'）

应该可以很好地工作。任何解决方案都会很好——哇，这太棒了。这很好，所以如果你把它作为答案提交，我会接受的。它取代了

Prefetch

对象，这正是我希望用于实现某种解耦预取的优雅解决方案的方法，但这确实很有效。谢谢