'Return data suitable for use in :meth:`has_book`. This can be used for an
implementation of :meth:`has_book` in a worker process without access to the
db.'

@read_api
def data_for_has_book(self):

    try:
        return {icu_lower(title) for title in self.fields[u'title'].table.book_col_map.itervalues()}
    except TypeError:
        return {icu_lower(as_unicode(title)) for title in self.fields[u'title'].table.book_col_map.itervalues()}
