'Returns the query object for this visualization'

def query_obj(self):

    d = super(HistogramViz, self).query_obj()
    d[u'row_limit'] = self.form_data.get(u'row_limit', int(config.get(u'VIZ_ROW_LIMIT')))
    numeric_column = self.form_data.get(u'all_columns_x')
    if (numeric_column is None):
        raise Exception(u'Must    have    one    numeric    column    specified')
    d[u'columns'] = [numeric_column]
    return d
