es_with_decay.py

from django.utils import timezone

from wagtail.wagtailsearch.backends.elasticsearch import ElasticSearch, ElasticSearchQuery

from wagtail.wagtailcore.models import Page
from wagtail.wagtailimages.models import AbstractImage
from wagtail.wagtaildocs.models import Document


class ElasticSearchQueryWithRecency(ElasticSearchQuery):
    """
    An elasticsearch query class that takes recency into account
    """
    def get_inner_query(self):
        if issubclass(self.queryset.model, Page):
            created_at_field = 'first_published_at_filter'
        elif issubclass(self.queryset.model, (AbstractImage, Document)):
            created_at_field = 'created_at_filter'
        else:
            created_at_field = None

        if created_at_field:
            return {
                "function_score": {
                    "query": super().get_inner_query(),
                    "functions": [
                        {
                            "gauss": {
                                created_at_field: {
                                    "origin": timezone.now(),
                                    "offset": "7d",
                                    "scale": "100d",
                                    "decay": 0.5,
                                }
                            }
                        }
                    ]
                }
            }
        else:
            return super().get_inner_query()


class CustomElasticSearch(ElasticSearch):
    search_query_class = ElasticSearchQueryWithRecency


SearchBackend = CustomElasticSearch