id,page,ref,title,content,breadcrumbs,references
plugin_hooks:plugin-register-facet-classes,plugin_hooks,plugin-register-facet-classes,register_facet_classes(),"Return a list of additional Facet subclasses to be registered. 
             
                 The design of this plugin hook is unstable and may change. See  issue 830 . 
             
             Each Facet subclass implements a new type of facet operation. The class should look like this: 
             class SpecialFacet(Facet):
    # This key must be unique across all facet classes:
    type = ""special""

    async def suggest(self):
        # Use self.sql and self.params to suggest some facets
        suggested_facets = []
        suggested_facets.append(
            {
                ""name"": column,  # Or other unique name
                # Construct the URL that will enable this facet:
                ""toggle_url"": self.ds.absolute_url(
                    self.request,
                    path_with_added_args(
                        self.request, {""_facet"": column}
                    ),
                ),
            }
        )
        return suggested_facets

    async def facet_results(self):
        # This should execute the facet operation and return results, again
        # using self.sql and self.params as the starting point
        facet_results = []
        facets_timed_out = []
        facet_size = self.get_facet_size()
        # Do some calculations here...
        for column in columns_selected_for_facet:
            try:
                facet_results_values = []
                # More calculations...
                facet_results_values.append(
                    {
                        ""value"": value,
                        ""label"": label,
                        ""count"": count,
                        ""toggle_url"": self.ds.absolute_url(
                            self.request, toggle_path
                        ),
                        ""selected"": selected,
                    }
                )
                facet_results.append(
                    {
                        ""name"": column,
                        ""results"": facet_results_values,
                        ""truncated"": len(facet_rows_results)
                        > facet_size,
                    }
                )
            except QueryInterrupted:
                facets_timed_out.append(column)

        return facet_results, facets_timed_out 
             See  datasette/facets.py  for examples of how these classes can work. 
             The plugin hook can then be used to register the new facet class like this: 
             @hookimpl
def register_facet_classes():
    return [SpecialFacet]","[""Plugin hooks""]","[{""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""}]"