Effiziente Join mit Django REST Framework Serialisierer

Question

Ich benutze die folgenden Reihe von Serialisierer zu erreichen, eine Join, die gut auf meine Entwicklung Setup funktionieren, führt aber schrecklich, wenn es einen Abstand zwischen dem Website-Server und dem Datenbankserver gibt. Ich wurde misstrauisch gegenüber dem SQL, das die Show ausführt, und habe etwas Logging gemacht; es scheint, dass es für jeden Eintrag eine neue Abfrage erstellt und die Ergebnisse kombiniert, anstatt den gesamten Join auf einmal durchzuführen und den Join wie gewünscht zurückzuschicken. Hier sind meine Serializer:

class UserSerializer(serializers.ModelSerializer): 
    class Meta: 
     model = User 
     exclude = ('password', 'last_login', 'is_superuser', 'is_staff', 'is_active', 'date_joined', 
        'groups', 'user_permissions') 


class DepartmentSerializer(serializers.HyperlinkedModelSerializer): 
    curator = UserSerializer() 
    class Meta: 
     model = Department 
     fields = '__all__' 


class CategorySerializer(serializers.HyperlinkedModelSerializer): 
    class Meta: 
     model = Category 
     fields = '__all__' 


class DetailedLinkedContentSerializer(serializers.HyperlinkedModelSerializer): 
    category = CategorySerializer() 
    department = DepartmentSerializer() 
    type = serializers.SerializerMethodField() 

    class Meta: 
     fields = '__all__' 
     model = LinkedContent 

    def get_type(self, obj): 
     return 'link' 


class DetailedFileContentSerializer(serializers.HyperlinkedModelSerializer): 
    category = CategorySerializer() 
    department = DepartmentSerializer() 
    link_url = serializers.SerializerMethodField() 
    type = serializers.SerializerMethodField() 

    class Meta: 
     fields = '__all__' 
     model = FileContent 

    def get_link_url(self, obj): 
     return obj.file.url 

    def get_type(self, obj): 
     return obj.file_type 

Wie Sie sehen können, ich tue meine ‚nachziehen‘ von Feldern in einem Serializer als Serializer anderer Modelle einschließlich, wie Kategorie = CategorySerializer(). Es sieht so aus, als ob DRF recommends, wenn ich etwas nicht falsch verstehe. Hier ist eine kleine Auswahl der Hunderte von Anfragen auf meiner Entwicklungsumgebung wird ausgeführt:

(0.001) SELECT "content_linkedcontent"."id", "content_linkedcontent"."link_text", "content_linkedcontent"."department_id", "content_linkedcontent"."category_id", "content_linkedcontent"."visibility_rank", "content_linkedcontent"."link_url" FROM "content_linkedcontent"; args=() 
(0.001) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 3; args=(3,) 
(0.001) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 24; args=(24,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 3; args=(3,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 3; args=(3,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 29; args=(29,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 4; args=(4,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 25; args=(25,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 1; args=(1,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 29; args=(29,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 1; args=(1,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 25; args=(25,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 1; args=(1,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 24; args=(24,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 3; args=(3,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 3; args=(3,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 28; args=(28,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 1; args=(1,) 
(0.000) SELECT "content_department"."id", "content_department"."name", "content_department"."description", "content_department"."curator_id", "content_department"."visibility_rank" FROM "content_department" WHERE "content_department"."id" = 28; args=(28,) 
(0.000) SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 6; args=(6,) 
(0.000) SELECT "content_category"."id", "content_category"."name", "content_category"."description" FROM "content_category" WHERE "content_category"."id" = 4; args=(4,) 

Wie kann ich eine echte verbinden mit den Informationen, die ich mit Serializer in DRF wollen?

UPDATE:

ich durch Anschluss an die Beratung auf this Blog-Eintrag haben verwalten, um die Abfragezeit in zwei Hälften geschnitten, hier meine aktualisiert Serializer und die Aussicht sind, die sie verwenden:

class DetailedLinkedContentSerializer(serializers.HyperlinkedModelSerializer): 
    category = CategorySerializer() 
    department_query = Department.objects.all() 
    department_query = DepartmentSerializer.setup_eager_loading(department_query) 
    department = DepartmentSerializer(department_query) 
    # department = DepartmentSerializer() 
    type = serializers.SerializerMethodField() 

    class Meta: 
     fields = '__all__' 
     model = LinkedContent 

    def get_type(self, obj): 
     return 'link' 

    @staticmethod 
    def setup_eager_loading(queryset): 
     """ Perform necessary eager loading of data. """ 
     queryset = queryset.select_related('category', 'department') 
     return queryset 


class DetailedFileContentSerializer(serializers.HyperlinkedModelSerializer): 
    category = CategorySerializer() 
    department_query = Department.objects.all() 
    department_query = DepartmentSerializer.setup_eager_loading(department_query) 
    department = DepartmentSerializer(department_query) 
    # department = DepartmentSerializer() 
    link_url = serializers.SerializerMethodField() 
    type = serializers.SerializerMethodField() 

    class Meta: 
     fields = '__all__' 
     model = FileContent 

    def get_link_url(self, obj): 
     return obj.file.url 

    def get_type(self, obj): 
     return obj.file_type 

    @staticmethod 
    def setup_eager_loading(queryset): 
     """ Perform necessary eager loading of data. """ 
     queryset = queryset.select_related('category', 'department') 
     return queryset 

und meine Ansicht, die Verwendung dieser Serializer macht:

class DetailedContentView(views.APIView): 
    permission_classes = [IsAuthenticated, ContentCuratorOrReadOnly, IsGroupMember, ] 
    def get(self, request, *args, **kwargs): 
     context = {"request": request} 
     linked_content = LinkedContent.objects.all() 
     file_content = FileContent.objects.all() 
     # this line is newly added 
     linked_content = DetailedLinkedContentSerializer.setup_eager_loading(linked_content) 
     # this line too 
     file_content = DetailedLinkedContentSerializer.setup_eager_loading(file_content) 
     linked_content_serializer = DetailedLinkedContentSerializer(linked_content, many=True, context=context) 
     file_content_serializer = DetailedFileContentSerializer(file_content, many=True, context=context) 

     response = linked_content_serializer.data + file_content_serializer.data 
     response = sorted(response, key=lambda x: (x['department']['visibility_rank'], x['visibility_rank'])) 

     return Response(response) 

jedoch meine Lösung prefetch meine Benutzer Serializer in meiner Abteilung Serializer scheint nicht mach den Trick. Insbesondere wird nach meiner Abteilung Serializer Aktualisierung:

class DepartmentSerializer(serializers.HyperlinkedModelSerializer): 
    curator = UserSerializer() 
    class Meta: 
     model = Department 
     fields = '__all__' 

    @staticmethod 
    def setup_eager_loading(queryset): 
     """ Perform necessary eager loading of data. """ 
     queryset = queryset.select_related('curator') 
     return queryset 

die folgenden Zeilen:

department_query = Department.objects.all() 
department_query = DepartmentSerializer.setup_eager_loading(department_query) 
department = DepartmentSerializer(department_query) 

scheinen nicht meine Kuratoren zu werden Prefetching, wie ich will.

class EagerLoadingMixin: 
    @classmethod 
    def setup_eager_loading(cls, queryset): 
     if hasattr(cls, "_SELECT_RELATED_FIELDS"): 
      queryset = queryset.select_related(*cls._SELECT_RELATED_FIELDS) 
     if hasattr(cls, "_PREFETCH_RELATED_FIELDS"): 
      queryset = queryset.prefetch_related(*cls._PREFETCH_RELATED_FIELDS) 
     return queryset 

und hinzugefügt 'department__curator' auf meine Liste der Prefetch-Felder:

Answer 1

ich meine Serializer mit einem mixin aus einem Kommentar in this blog gefunden aktualisiert. Jetzt sieht es so aus:

Die Abfrage dauert jetzt etwa 1/3 der Zeit und enthält nicht Hunderte von SELECTs. Es dauert noch zu lange, aber ich glaube, dass ich das lösen kann, indem ich auf eine andere Hosting-Lösung für meine Datenbank umschalte.