python - django taggit similar_objects 查询非常慢

Question

我正在尝试选择 3 个最近发布的项目，其中任何标签都与当前项目相似(以及其他一些过滤器)找不到有效的方法，数据库中有很多“项目”。

from taggit_autosuggest.managers import TaggableManager

class Item(models.Model):
    publish_date = DateField()
    tags = TaggableManager()
    sites = ManyToManyField(Site)

def my_view():
    ...
    current_item = #get current item
    related_items = Item.active_objects.filter(
        sites=current_site,
        id__in=[x.id for x in current_item.tags.similar_objects()]
        ).order_by('-publish_date')[:3]
    ...

但这会导致相当大的性能问题，来自 similar_objects() 方法。 current_item 拥有的标签越多，指数越差

# Query_time: 20.613503  Lock_time: 0.000182 Rows_sent: 83  Rows_examined: 7566504
SELECT `taggit_taggeditem`.`content_type_id`, `taggit_taggeditem`.`object_id`, COUNT(`taggit_taggeditem`.`id`) AS `n` FROM `taggit_taggeditem` WHERE (NOT (`taggit_taggeditem`.`object_id` = 205636  AND `taggit_taggeditem`.`content_type_id`
 = 11 ) AND (`taggit_taggeditem`.`tag_id`) IN (SELECT DISTINCT `taggit_tag`.`id` FROM `taggit_tag` INNER JOIN `taggit_taggeditem` ON ( `taggit_tag`.`id` = `taggit_taggeditem`.`tag_id` ) WHERE (`taggit_taggeditem`.`object_id` = 205636  AND
 `taggit_taggeditem`.`content_type_id` = 11 ))) GROUP BY `taggit_taggeditem`.`content_type_id`, `taggit_taggeditem`.`object_id` ORDER BY `n` DESC;

我也试过不使用相似对象方法

related_items = Item.active_objects.filter(
    sites=current_site,
    tags__in=current_item.tags.all()).exclude(slug=slug).order_by('-publish_date').distinct()[:3]
    context['tagged'] = tags.order_by('-publish_date').distinct()[:3] 

这一直很糟糕(有些查询长达 120 秒，糟糕)

执行此操作的“好”方法是什么？!

Answer 1

我的假设是获取标签并使用标签-> 项目关系比搜索所有项目更有效。所以我们构建了一个包含所有 TaggedItem 的查询集，获取所有对象的 ID，然后执行我们的过滤器。

from taggit.models import TaggedItem
related_items = TaggedItem.objects.none()
for tag in current_item.tags.all():
    #build queryset of all TaggedItems
    related_items |= tag.taggit_taggeditem_items.all()

#TaggedItem doesn't have a direct link to the object, have to grab ids
ids = related_items.values_list('object_id', flat=True)
return Item.objects.filter(id__in=ids, sites=current_site).exclude(id=item.id).order_by('-publish_date')[:3]