Django Haystack Index definition after using custom code

my_model_index.py

class MyModelIndex(AutoPrepareTextIndexMixin, CelerySearchIndex, indexes.Indexable):
    model_pk = indexes.IntegerField(model_attr='pk')  # This is required
    text = indexes.EdgeNgramField(document=True)  # This too
    some_boolean = indexes.IntegerField(model_attr='some_boolean')

    # Filters should map to the exact field name that the admin will access them by.
    # Example: foreign keys are accessed by FKModel__id. This is for filters
    rel_model = indexes.IntegerField(model_attr='rel_model__id')

    document_fields = ['name', 'nickname', 'rel_model__title']  # ^_^
    select_related_for_index = ['business']

    def get_model(self):
        return MyModel