我有 2 个模型, Author 和 Post ,我如何制作一个过滤器,可以在一行中选择每个 Author 的最后一篇文章(通过 id 字段)?,对我来说不好的方法是:
authors = Author.objects.all()
queryset = []
for author in authors:
posts = Post.objects.filter(author=author).order_by('-id')
if loc:
queryset.append(posts[0])
具体来说,这是为了过滤我的 Tastypie 资源“PostResource”,这个过滤器只能给我每个用户的最后一篇帖子,按创建排序
带有 okm answer 和 tastypie 自定义过滤器的完整解决方案:
class LocationResource(ModelResource):
user = fields.ForeignKey(AccountResource,'user' )
class Meta:
queryset = Location.objects.all().order_by('-id')
resource_name = 'location'
#excludes = ['id',]
list_allowed_methods = ['post','get']
authentication = ApiKeyAuthentication()
authorization= Authorization()
filtering = {'user': ALL_WITH_RELATIONS}
def obj_create(self, bundle, **kwargs):
if bundle.request.method == 'POST':
return super(LocationResource, self).obj_create(bundle, user=bundle.request.user)
def apply_authorization_limits(self, request, object_list):
return object_list.filter(user=request.user)
def dehydrate(self, bundle):
return bundle
def build_filters(self, filters=None):
if filters is None: #if you don't pass any filters at all
filters = {}
orm_filters = super(LocationResource, self).build_filters(filters)
if('only_lasts' in filters):
query = filters['only_lasts']
sqs = Location.objects.values('user_id').annotate(max_id=models.Max('id')).values('max_id')
orm_filters["pk__in"] = sqs
return orm_filters
最佳答案
阅读the blog post关于在 SQL 中按组获取第一行。
如帖子中所述,您可以使用 IN
或 JOIN
。
以IN
为例:
SELECT * FROM post_table
WHERE id IN (SELECT MAX(id) AS max_id FROM post_table GROUP BY author_id);
SQL 可以用 QuerySet 写成:
Post.objects.filter(pk__in=
Post.objects.order_by().values('author_id').annotate(
max_id=models.Max('id')).values('max_id'))
SELECT MAX(id) AS max_id FROM post_table GROUP BY author_id
的QuerySet
模式是:
Model.objects.order_by().values(...).annotate(foo=...).values('foo')
^------------^----------^-----------^-----------------^------------^
\ \ \ \ \
base queryset \ GROUP BY \ SELECT column
or manager remove possible annotation part
useless ordering Min/Max/...
此外,您可以直接将 SQL 包装在 queryset.raw()
中。如果选择JOIN
版本,.raw()
方式更清晰。
请注意,IN
子句在您的数据库后端可能存在性能问题,如果性能至关重要,您需要分析和调整索引。
关于django - 在 django : the last post of each user 中过滤,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16074498/