MyBatisSystemException异常产生原因及解决方案

01 异常发生场景

• 当我使用mybatis对数据库操作时报的错误

<resultMap id="shoppingCartProduct" type="shoppingCartProductVo">
        <id property="shoppingCartId" column="shopping_cart_id"></id>
        <result property="productId" column="product_id"></result>
        <result property="num" column="num"></result>
        <result property="productName" column="product_name"></result>
        <result property="productTitle" column="product_title"></result>
        <result property="productIntro" column="product_intro"></result>
        <result property="productPicture" column="product_picture"></result>
        <result property="productPrice" column="product_price"></result>
        <result property="productSellingPrice" column="product_selling_price"></result>
    </resultMap>
    <select id="selectShoppingCartByIds" resultMap="shoppingCartProduct">
        select
            s.shopping_cart_id,
            s.num,
            s.product_id,
            p.product_name,
            p.product_title,
            p.product_intro,
            p.product_picture,
            p.product_price,
            p.product_selling_price
            FROM
            shopping_cart AS s
            left JOIN
            product AS p
            ON s.product_id = p.product_id
            WHERE
            s.shopping_cart_id 
            in (<foreach collection="list" index="id" separator=",">
                #{id}
            </foreach>)
    </select>

02 尝试解决问题的过程

1.事务问题

• 一开始，我以为是事务问题，于是在service层加上了@Transactional开启事务

@Override
@Transactional
public GetData postOrders(List<Long> shoppingCartIds, Long userId) {
    //1.判断用户是否存在
    if (msUserMapper.FindUser(userId) == null) {
        GetData getData=new GetData(500,"无此账号",null);
        return getData;
    }
    //2.生成订单
    Orders orders=new Orders();
    orders.setOrderNum(UUID.randomUUID().toString());
    orders.setUserId(userId);
    orders.setOrderTime(new Date());
    orderProductMapper.addOrders(orders);
    System.out.println(orders.getOrderId());
    System.out.println(orders.getOrderId().getClass().getTypeName());
    System.out.println(shoppingCartIds);

    //3.查询购物车商品数据
    List<ShoppingCartProductVo> shoppingCartProductVos = productMapper.selectShoppingCartByIds(shoppingCartIds);
    System.out.println(shoppingCartProductVos.size());
    System.out.println(shoppingCartProductVos);
    List<OrdersDtl> ordersDtls = new ArrayList<>();
    for (ShoppingCartProductVo vo : shoppingCartProductVos) {
        OrdersDtl ordersDtl = new OrdersDtl();
        ordersDtl.setOrderId(orders.getOrderId());
        ordersDtl.setProductId(vo.getProductId());
        ordersDtl.setProductIntro(vo.getProductIntro());
        ordersDtl.setProductName(vo.getProductName());
        ordersDtl.setProductPicture(vo.getProductPicture());
        ordersDtl.setProductPrice(vo.getProductPrice());
        ordersDtl.setProductSellingPrice(vo.getProductSellingPrice());
        ordersDtl.setProductTitle(vo.getProductTitle());
        ordersDtl.setNum(vo.getNum());
        ordersDtls.add(ordersDtl);
    }
    System.out.println(ordersDtls);
    orderProductMapper.addBatchOrderDtlsInt(ordersDtls);
    System.out.println(1);
    int rs =shoppingCartMapper.deleteShoppingCarts(shoppingCartIds);

    if (rs>0){
        GetData getData=new GetData(200,"操作成功",null);
        return getData;
    }else {
        GetData getData=new GetData(500,"操作成功",rs);
        return getData;
    }

}

• 现在想想，真是没抓住重点，看错了代码的报错信息

2.MyBatis一级缓存问题

• 接着排查发现发现查询出的数据与同样的代码在数据库里不一样，人当场傻了
• 面向百度编程后认为是出现了MyBatis一级缓存问题
• 于是在yml文件中关闭关闭了MyBatis一级缓存

# 配置mybatis
mybatis:
  # mapper配置文件
  mapper-locations: classpath:mapper/*.xml
  # resultType别名，没有这个配置resultType包名要写全，配置后只要写类名
  type-aliases-package: com.example.demo.com.mashang.dao
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    map-underscore-to-camel-case: true
    local-cache-scope: statement # 设置一级缓存关闭，mybatis默认开启

• 当然还是不对，无可奈何之下，我只能回归最初的报错信息，意思大概是文件映射有问题

03 问题的产生及其原因

• 没办法，如果真是映射出了错，那就只能一个一个排查过去了
• 终于在结合了springboot的报错日志
• log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

select 
s.num, s.product_id, p.product_name, p.product_title, p.product_intro, p.product_picture, p.product_price, p.product_selling_price 
FROM shopping_cart AS s 
INNER JOIN product AS p 
ON s.product_id = p.product_id 
WHERE s.shopping_cart_id 
in ( ? , ? , ? )

• 终于，我发现mybatis执行的语句中，三个问号插入的值是固定的0,1,2
• 也就是循环插入出了问题
• 果然，我错误的使用了标签index

04 解决方式

• 只要认真检查mybatis的映射文件，我的话是把标签换成即可，以下是修改后的mybatis映射文件

<resultMap id="shoppingCartProduct" type="shoppingCartProductVo">
    <id property="shoppingCartId" column="shopping_cart_id"></id>
    <result property="productId" column="product_id"></result>
    <result property="num" column="num"></result>
    <result property="productName" column="product_name"></result>
    <result property="productTitle" column="product_title"></result>
    <result property="productIntro" column="product_intro"></result>
    <result property="productPicture" column="product_picture"></result>
    <result property="productPrice" column="product_price"></result>
    <result property="productSellingPrice" column="product_selling_price"></result>
</resultMap>
<select id="selectShoppingCartByIds" resultMap="shoppingCartProduct">
    select
        s.shopping_cart_id,
        s.num,
        s.product_id,
        p.product_name,
        p.product_title,
        p.product_intro,
        p.product_picture,
        p.product_price,
        p.product_selling_price
        FROM
        shopping_cart AS s
        left JOIN
        product AS p
        ON s.product_id = p.product_id
        WHERE
        s.shopping_cart_id 
        in (<foreach collection="list" item="id" separator=",">
            #{id}
        </foreach>)
</select>