'Accepts an arbitrary number of Model classes to include in the search.'

def models(self, *models):

    clone = self._clone()
    for model in models:
        if (model not in connections[self.query._using].get_unified_index().get_indexed_models()):
            warnings.warn((u'The    model    %r    is    not    registered    for    search.' % (model,)))
        clone.query.add_model(model)
    return clone
