如何通过单条查询获取关联的Tag对象？

模型定义： #

class Tag(BaseModel):
    tag_name = models.CharField(max_length=250)
    slug = models.SlugField()

    def save(self, *args, **kwargs):
        self.slug = slugify(self.tag_name)
        super(Tag, self).save(*args, **kwargs)

    def __str__(self):
        return str(self.tag_name)


class Tags(BaseModel):
    filtertype = models.CharField(max_length=250)
    tags = models.ManyToManyField(Tag)

当前实现（两条查询）： #

def get(self,request,version):
    filtertype = request.query_params.get('filtertype', '')
    filtertypes = filtertype.split(",")

    tagsList = Tags.objects.filter(filtertype__in=filtertypes).values_list('tags', flat=True).distinct()
    queryset = Tag.objects.filter(id__in=tagsList)

    context = {"request": request}
    serialized = TagListSerializers(queryset, many=True, context=context)
    return Response(serialized.data)

直接利用Django的跨表关联查询能力，通过Tag模型反向关联Tags表，一次查询即可获取目标数据：

def get(self,request,version):
    filtertype = request.query_params.get('filtertype', '')
    filtertypes = filtertype.split(",")

    # 单条跨表查询，自动去重避免重复Tag
    queryset = Tag.objects.filter(tags__filtertype__in=filtertypes).distinct()

    context = {"request": request}
    serialized = TagListSerializers(queryset, many=True, context=context)
    return Response(serialized.data)

说明： #

• tags__filtertype__in=filtertypes：通过Tag模型的反向关联（对应Tags表的tags字段），直接过滤出关联filtertype符合条件的Tag对象
• .distinct()：因为多对多关联可能导致同一Tag被多次匹配，用这个方法去重，保证结果唯一性

内容的提问来源于stack exchange，提问作者V. Bujdosó