具有 collated/merged 个值的查询集

Question

假设我有以下两个模型：

class Parent(models.Model):
    name = models.CharField(max_length=48)

class Child(models.Model):
    name = models.CharField(max_length=48)
    movement = models.ForeignKey(Parent, related_name='children')

我有以下 DRF generics.ListAPIView，我希望能够在 Child 对象上 search/filter 但实际上 return 相关的 Parent 对象:


class ParentSearchByChildNameView(generics.ListAPIView):
    """
    Return a list of parents who have a child with the given name
    """
    serializer_class = ParentSerializer

    def get_queryset(self):
        child_name = self.request.query_params.get('name')

        queryset = Child.objects.all()
        if child_name is not None:
            queryset = queryset.filter(name__contains=child_name)

        matched_parents = Parent.objects.filter(children__in=queryset).distinct()
        return matched_parents

现在，这对我来说效果很好。如果一个 Parent 对象有 3 个 Child 对象，它们都匹配给定的“名称”query_param，那么我只得到一个 Parent 对象，这就是我想要的：

{
    "next": null,
    "previous": null,
    "results": [
        {
            "url": "URL to parent",
            "name": "Parent #1",
        }
    ]
}

但是，我还想要在结果中指示匹配的 Child 对象 ID。如果我可以在 JSON 中说明我想要什么：

{
    "next": null,
    "previous": null,
    "results": [
        {
            "url": "URL to parent",
            "name": "Parent #1",
            "matched_child": [1, 3, 7]
        }
    ]
}

这是我可以使用内置工具完成的事情，而无需昂贵且反复访问数据库吗？

Answer 1

如果您与 postgresql, you can work with an ArrayAgg expression [Django-doc] 一起工作：

from django.contrib.postgres.aggregates import <b>ArrayAgg</b>

class ParentSearchByChildNameView(generics.ListAPIView):
    """
    Return a list of parents who have a child with the given name
    """
    serializer_class = ParentSerializer

    def get_queryset(self):
        child_name = self.request.query_params.get('name')
        return = Parent.objects.filter(
            children__name__contains=child_name
        ).annotate(<strong>matched_children=ArrayAgg('children__pk')</strong>)

在序列化程序中，您因此添加了一个 ListField，它将列出子项：

class ParentSerializer(serializers.ModelSerializer)
    <strong>matched_children</strong> = serializers.ListField(
        child=serializers.IntegerField(),
        read_only=True
    )

    class Meta:
        model = Parent
        fields = ['url', 'name', <strong>'matched_children'</strong>]

Answer 2

在不使用特定于数据库的功能的情况下，您可以使用 Prefetch object [Django-doc]:

from django.db.models import Prefetch

class ParentSearchByChildNameView(generics.ListAPIView):
    """
    Return a list of parents who have a child with the given name
    """
    serializer_class = ParentSerializer

    def get_queryset(self):
        child_name = self.request.query_params.get('name')
        return = Parent.objects.filter(
            children__name__contains=child_name
        ).prefetch_related(
            <strong>Prefetch('children', Child.objects.filter(name=child_name), to_attr='matched_children')</strong>
        ).distinct()

对于序列化程序，我们可以使用 PrimaryKeyRelatedField [drf-doc]:

class ParentSerializer(serializers.ModelSerializer)
    matched_children = serializers.<strong>PrimaryKeyRelatedField(</strong>
        many=True,
        read_only=True
    <strong>)</strong>

    class Meta:
        model = Parent
        fields = ['url', 'name', <strong>'matched_children'</strong>]

具有 collated/merged 个值的查询集

Queryset with collated/merged values

python

django

django-models

django-rest-framework