docs: async def filter(self, request):
          """Filter collection."""
          collection = self.collection
          self.filter_form.process(request.query)
          data = self.filter_form.data
          self.filter_form.active = any(o and o is not DEFAULT for o in data.values())
          for flt in self.columns_filters:
              try:
                  collection = flt.apply(collection, data)
              # Invalid filter value
              except ValueError:
                  continue
          return collection