如何在 django 中优先搜索？答案

【问题标题】：How to do search with priority in django?如何在 django 中优先搜索？
【发布时间】：2020-12-02 05:56:32
【问题描述】：

我正在使用 djangorestframework 和 mysql 数据库。我有一个基于搜索查询参数返回列表的视图。我正在使用 rest_frameworks.filters SearchFilter 进行基于搜索的过滤。这是我的看法：

from rest_framework import filters
from rest_framework.generics import ListAPIView
...

class FooListView(ListAPIView):
    serializer_class = SymbolSerializer
    queryset = Symbol.objects.all()
    filter_backends = [filters.SearchFilter]
    search_fields = ['field_A', 'field_B', 'field_C']

要调用的示例 URL 是：

http://localhost:8000/symbols/symbols/?search=bird

现在一切正常，但我需要一个 filters.SearchFilter 不支持的功能。我希望我的搜索按 search_fields 的优先级排序。

例如这里有两条记录：

foo1 : {"field_A": "any", "field_B": "many", "field_C": "bar", "id": 3}

foo2 : {"field_A": "many", "field_B": "any", "field_C": "bar", "id": 4}

现在，当我使用 search='many' 参数进行搜索时，我希望视图返回一个列表，其中 foo2 记录高于 foo1（如 [foo2, foo1] ），因为我希望搜索的优先级是 field_A score 但它只返回一个按 id ([foo1, foo2]) 排序的列表。

有什么帮助吗？

【问题讨论】：

标签： mysql django django-rest-framework django-filter django-rest-framework-filters

【解决方案1】：

我只是偶然发现了同样的问题。

我的解决方案是使用来自this response 的灵感稍微调整 DRF 的filters.SearchFilter 的搜索逻辑，并最终得到以下自定义过滤器类：

class PriorizedSearchFilter(filters.SearchFilter):
    def filter_queryset(self, request, queryset, view):
        """Override to return priorized results."""
        # Copy paste from DRF
        search_fields = getattr(view, 'search_fields', None)
        search_terms = self.get_search_terms(request)

        if not search_fields or not search_terms:
            return queryset

        orm_lookups = [
            self.construct_search(six.text_type(search_field))
            for search_field in search_fields
        ]
        base = queryset
        conditions = []

        # Will contain a queryset for each search term
        querysets = list()

        for search_term in search_terms:
            queries = [
                models.Q(**{orm_lookup: search_term})
                for orm_lookup in orm_lookups
            ]

            # Conditions for annotated priority value. Priority == inverse of the search field's index.
            # Example: 
            #   search_fields = ['field_A', 'field_B', 'field_C']
            #   Priorities are field_A = 2, field_B = 1, field_C = 0
            when_conditions = [models.When(queries[i], then=models.Value(len(queries) - i - 1)) for i in range(len(queries))]
            
            # Generate queryset result for this search term, with annotated priority
            querysets.append(
                queryset.filter(reduce(operator.or_, queries))
                    .annotate(priority=models.Case(
                        *when_conditions,
                        output_field=models.IntegerField(),
                        default=models.Value(-1)) # Lowest possible priority
                    )
                )

        # Intersect all querysets and order by highest priority
        queryset = reduce(operator.and_, querysets).order_by('-priority')

        # Copy paste from DRF
        if self.must_call_distinct(queryset, search_fields):
            # Filtering against a many-to-many field requires us to
            # call queryset.distinct() in order to avoid duplicate items
            # in the resulting queryset.
            # We try to avoid this if possible, for performance reasons.
            queryset = distinct(queryset, base)
        return queryset

使用 filter_backends = [PrioritizedSearchFilter] 就可以了。

【讨论】：