{"id": "plugin_hooks:plugin-register-facet-classes", "page": "plugin_hooks", "ref": "plugin-register-facet-classes", "title": "register_facet_classes()", "content": "Return a list of additional Facet subclasses to be registered. \n             \n                 The design of this plugin hook is unstable and may change. See  issue 830 . \n             \n             Each Facet subclass implements a new type of facet operation. The class should look like this: \n             class SpecialFacet(Facet):\n    # This key must be unique across all facet classes:\n    type = \"special\"\n\n    async def suggest(self):\n        # Use self.sql and self.params to suggest some facets\n        suggested_facets = []\n        suggested_facets.append(\n            {\n                \"name\": column,  # Or other unique name\n                # Construct the URL that will enable this facet:\n                \"toggle_url\": self.ds.absolute_url(\n                    self.request,\n                    path_with_added_args(\n                        self.request, {\"_facet\": column}\n                    ),\n                ),\n            }\n        )\n        return suggested_facets\n\n    async def facet_results(self):\n        # This should execute the facet operation and return results, again\n        # using self.sql and self.params as the starting point\n        facet_results = []\n        facets_timed_out = []\n        facet_size = self.get_facet_size()\n        # Do some calculations here...\n        for column in columns_selected_for_facet:\n            try:\n                facet_results_values = []\n                # More calculations...\n                facet_results_values.append(\n                    {\n                        \"value\": value,\n                        \"label\": label,\n                        \"count\": count,\n                        \"toggle_url\": self.ds.absolute_url(\n                            self.request, toggle_path\n                        ),\n                        \"selected\": selected,\n                    }\n                )\n                facet_results.append(\n                    {\n                        \"name\": column,\n                        \"results\": facet_results_values,\n                        \"truncated\": len(facet_rows_results)\n                        > facet_size,\n                    }\n                )\n            except QueryInterrupted:\n                facets_timed_out.append(column)\n\n        return facet_results, facets_timed_out \n             See  datasette/facets.py  for examples of how these classes can work. \n             The plugin hook can then be used to register the new facet class like this: \n             @hookimpl\ndef register_facet_classes():\n    return [SpecialFacet]", "breadcrumbs": "[\"Plugin hooks\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette/issues/830\", \"label\": \"issue 830\"}, {\"href\": \"https://github.com/simonw/datasette/blob/main/datasette/facets.py\", \"label\": \"datasette/facets.py\"}]"}