@Override
public?ItemModel?getItemById(Integer?id)?{
????ItemDo?itemDo?=?itemDoMapper.selectByPrimaryKey(id);
????if?(itemDo?==?null)?{
????????return?null;
????}
????//操作獲得庫存的數量
????//！?。。?！返回為空指針
????ItemStockDo?itemStockDo?=?itemStockDoMapper.selectByItemId(itemDo.getId());

????//將dataObject->Model
????ItemModel?itemModel?=?convertFromObject(itemDo,?itemStockDo);


????return?itemModel;
}

<select?id="selectByItemId"?parameterType="java.lang.Integer"?resultMap="BaseResultMap">
????select
????<include?refid="Base_Column_List"/>
????from?item_stock
????where?item_id?=?#{itemId,jdbcType=INTEGER}
</select>