@classmethod
def add_main_fields_names_from_nested(cls, fields):
    """If you add main_field__secondary_field, main_field should also be in the set."""
    to_add = set()
    for field in fields:
        parts = field.split('__', 1)
        if len(parts) == 2:
            to_add.add(parts[0])
    return fields | to_add
