class_id是保留字吗？uni-data-picker显示一直报错

<uni-data-picker v-model="class_id" collection="XXXXX"
field="class_id as value, name as text" :where="sWhere" />

在field里用class_id as value，显示就一直报错"SYSTEM_ERROR: Unexpected token (1:42)"
换成其他字段就不会。