Django rest framework 简单模型序列化器列表视图永远显示 10 条记录

Question

我有这个模型 -

class News(BaseEntityBasicAbstract, HitCountMixin):
    """
    News added from the dashboard with content
    """
    NEWS_STATUS = (
        ('draft', _('Draft')),
        ('pending', _('Pending')),
        ('review', _('Review')),
        ('public', _('Public')),
        ('private', _('Private'))
    )
    backup = models.BooleanField(default=False)
    prev_id = models.BigIntegerField(null=True, blank=True)
    language = models.CharField(max_length=10, choices=LANGUAGES, default='bn', db_index=True)
    heading = models.CharField(max_length=255, null=True, blank=True,
                               verbose_name=_('News Heading'),
                               help_text=_('Provide a news heading/caption.'))
    sub_caption = models.TextField(max_length=255, null=True, blank=True,
                                   verbose_name=_('Summary'),
                                   help_text=_('Provide summary of the news.'))
    url = models.CharField(max_length=255, unique=True, verbose_name=_('URL/Slug/Link'),
                           help_text=_('Unique url for the news without whitspace.'))
    content = HTMLField(null=True, blank=True, verbose_name=_('Content'),
                        help_text=_('HTML content with texts, links & images.'))
    featured_image = models.FileField(upload_to=FilePrefix('news/'), null=True, blank=True,
                                      verbose_name=_('Featured Image'),
                                      help_text=_('Upload a featured image for news.'))
    image_caption = models.TextField(max_length=255, null=True, blank=True,
                                     verbose_name=_('Image Caption'),
                                     help_text=_('Provide a image caption.'))
    status = models.CharField(max_length=20, choices=NEWS_STATUS, default='pending',
                              verbose_name=_('News Status'), db_index=True,
                              help_text=_('Only public news can be seen on front end.'))
    source = models.ForeignKey(NewsSource, on_delete=models.SET_NULL, null=True, blank=True,
                               verbose_name=_('News Source'),
                               help_text=_('Select a news source.'))
    category = models.ForeignKey(Category, on_delete=models.SET_NULL, null=True, blank=True,
                                 verbose_name=_('Category'),
                                 help_text=_('Select a news category.'))
    tags = tagulous.models.TagField(
        blank=True,
        to=Tags,
        verbose_name=_('News Tags'),
        help_text=_('Provide news tags separated with commas.')
    )
    published_at = models.DateTimeField(null=True, blank=True, db_index=True,
                                        verbose_name=_('Published At'))
    menu_items = GenericRelation(MenuItems, object_id_field='id',
                                 related_query_name='news_as_menu')
    hit_count_generic = GenericRelation(HitCount, object_id_field='object_pk',
                                        related_query_name='news_hit_count')
    created_by = models.ForeignKey(User, related_name='news_created_by',
                                   on_delete=models.SET_NULL, null=True, blank=True,
                                   verbose_name=_('Created By'))
    updated_by = models.ForeignKey(User, related_name='news_updated_by',
                                   on_delete=models.SET_NULL, null=True, blank=True,
                                   verbose_name=_('Last Updated By'))
    published_by = models.ForeignKey(User, related_name='news_published_by',
                                     on_delete=models.SET_NULL, null=True, blank=True,
                                     verbose_name=_('Published By'))
    deleted_by = models.ForeignKey(User, related_name='news_deleted_by',
                                   on_delete=models.SET_NULL, null=True, blank=True,
                                   verbose_name=_('Deleted By'))

下面是序列化程序 -

class NewsSerializer(serializers.ModelSerializer):
    class Meta:
        model = News
        fields = ['id', 'heading', 'sub_caption', 'url', 'content', 'featured_image',
                  'image_caption', 'category', 'source', 'tags', 'published_at']

这是视图 -

class NewsViewSets(viewsets.ModelViewSet):
    queryset = News.objects.filter(
        is_active=True,
        status='public'
    )
    serializer_class = NewsSerializer

    def get_queryset(self):
        queryset = self.queryset.filter(
            language=self.request.LANGUAGE_CODE
        ).order_by('-id')

        return queryset

分页在settings.py中设置为仅10，当我点击新闻api url时，仅加载10条记录需要9/10秒。这是显示 django-debug-toolbar 报告的屏幕截图 -

我在数据库中有大约 40 万条记录 table，这可能是个问题，但我认为加载时间太长了。请帮我找到这里的问题！提前致谢。

Answer 1

过滤通常很慢。看起来您在相关字段上有数据库索引，但请注意，如果您有多个过滤器，则只会使用其中一个索引。

我是根据您的专栏猜测的，但似乎最常见的查询总是寻找 is_active=1 和 status='public'。如果不是这种情况，您可能需要进行一些调整。

首先，删除 status、is_active 和 language 字段上的 db_index=True，否则您的数据库写入会不必要地变慢。

那么你可以制定这样的索引：

class Meta:
    indexes = [
        models.Index(
            fields=["is_active", "status", "language"],
            name="idx_filtering",
        )
    ]

当您一次过滤所有三列时，这将有助于数据库。但是，如果您只对其中一列进行过滤，您可能希望保留原始 db_index=True.

如果您使用的是 PostgreSQL，您可以做得更好：

class Meta:
    indexes = [
        models.Index(
            fields=["is_active", "status", "language"],
            name="idx_filtering",
            condition=Q(is_active=True, status="public"),
        )

这会将索引的大小减小到仅匹配 Q() 的索引，从而加快遍历速度。

另一件需要注意的事情是，一旦你达到更高的偏移量，使用 OFFSET 的分页就会非常慢。如果可能的话，您应该改用 DRF 的光标分页。

Django rest framework 简单模型序列化器列表视图永远显示 10 条记录

Django rest framework simple model serializer list view takes forever to show 10 records

python

django

performance

django-rest-framework

django-debug-toolbar