Keep top level facet counts when drilling down in haystack

views.py

from haystack.views import FacetedSearchView

class StickyFacetedSearchView (FacetedSearchView):

    def top_level_facets(self):
        """
        When selecting a facet to drill down the results, 
        we need to keep the top level facet counts
        """
        stored_query = self.request.session.get('query', None)

        if stored_query != self.query:
            self.request.session['query'] = self.query
            self.request.session['facet_counts'] = self.results.facet_counts()

        return self.request.session['facet_counts'] # Fail loudly

    def extra_context(self):
        """ add base_facets to extra_context"""
        extra = super(StickyFacetedSearchView, self).extra_context()
        extra['base_facets'] = self.top_level_facets()
        return extra