django orm 最新项目组按每个外键

debugcn 发表于 Dev

马赫迪

我们有以下型号：

class Publisher(models.Model):
    name = models.CharField(max_length=32)
    local_name = models.CharField(max_length=32)
    url_pattern = models.CharField(max_length=128)
    enabled = models.BooleanField(default=True)
    home_page = models.BooleanField(default=False)
    category = models.ForeignKey(NewspaperCategory, null=True)


class Newspaper(models.Model):
    class Meta:
        unique_together = ("publisher", "date")
        ordering = ("-date",)

    publisher = models.ForeignKey(Publisher)
    image = models.ImageField(upload_to=newspaper_upload_to)
    thumbnail = models.ImageField(upload_to=newspaper_thumbnail_upload_to)
    date = models.DateField()

我有一个APIView（Django rest 框架）并且有几个不同的查询参数可以过滤 API 的输出。我想要一个“最新”查询参数，它只列出每个发布者的最新版本。此外，QuerySet在评估之前，我需要能够对其进行进一步过滤和切片。

但是查询的结果应该是 Newspaper 实例，而不是dict这样我可以将它们提供给我的序列化程序。目前我的观点是这样的：

class Newspapers(APIView):
    def get(self, request):

        queryset = models.Newspaper.objects.filter(deleted=False).prefetch_related('publisher')
        if "latest" in request.GET:
            # doing something here with queryset            
        if "publisher_id" in request.GET:
            queryset = queryset.filter(publisher_id=request.GET['publisher_id'])
        if "category" in request.GET:
            queryset = queryset.filter(publisher__category_id=request.GET['category'])
        if "before" in request.GET:
            queryset = queryset.filter(date__lt=request.GET['before'])
        if "after" in request.GET:
            queryset = queryset.filter(date__gte=request.GET['after'])
        if "home_page" in request.GET:
            queryset = queryset.filter(publisher__home_page=request.GET['home_page'].lower() == 'true')
        queryset = queryset.order_by('-date', 'publisher__order')
        return PagingResponse(
            request,
            serializers.NewspaperVersionSerializer,
            query=queryset,
            identifier_name='date'
        )

马赫迪

我们可以通过两个查询来做到这一点：

        if "latest" in request.GET:
            latest_ids = list(  # <-- first query
                           queryset.order_by('id') 
                          .values('publisher_id')
                          .annotate(id=Max('id'))
                          .values_list('id', flat=True)
                          )
            queryset = queryset.filter(id__in=latest_ids) # <-- second query

第一个查询按出版商获取最新报纸组的列表，第二个查询获取这些报纸的查询集，以便进一步过滤、切片和...

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