日常报错记录2: MyBatis:DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.------------ Cause: java.lang.NoSuchMethodException: com.offcn.dao.ShopDao.<init>()

 

 直接上干货:

 报错归纳1:

 DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.

原因:xml里面不能有java方不存在的类,它是会去找的,找不到就报错,所以,万一删掉java类了,xml里面的相对应映射的字段也要注释掉。遇到两次了!浪费不少时间!

 

2.MyBatis     他要加空构造   实例化对象

原因:MyBitis ,他实体类pojo  class里 要加空构造

 

 

 

3.写法

 

 

 class 是点,路径是斜杠

 

 

 

 

4.

xml 控制多级级联查数据库,是可以的,(MyBatis xml作为实现 数据库查询),我这里四级连着查询

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.XXXX.dao.ShopDao">


<!--private int sid;

    private String sname;

    private List<Book> blist;-->

<resultMap id="resultMap_shop" type="shop">

    <id property="sid" column="sid"></id>
    <result property="sname" column="sname" ></result>

    <collection property="blist"  ofType="book">
        <id property="bid" column="bid"></id>
        <result property="bname" column="bname"></result>

            <association property="user" javaType="user">
                <id property="uid" column="uid"></id>
                <result property="uname" column="uname"></result>
                <result property="password" column="password"></result>

                <association property="p" javaType="person" >
                    <id property="pid" column="pid"></id>
                    <result property="pname" column="pname"></result>
                    <result property="sex" column="sex"></result>
                    <result property="birthday" column="birthday"></result>
                </association>

            </association>

    </collection>
   <!-- <association property="blist" javaType=""-->
</resultMap>

<!-- List<Shop> getAll(int sid);-->

    <select id="getAll" parameterType="int" resultMap="resultMap_shop">
      select from t_shop s,t_book b,t_user u,t_person p where u.user_person_fk=p.pid and b.book_user_fk=u.uid and s.sid=#{sid}

    </select>




</mapper>

 

5.

Cause: java.lang.NoSuchMethodException: com.offcn.dao.ShopDao.<init>(),其实是缺少构造,但构造没问题,之后发现是这个写错

 

posted @ 2019-03-14 23:58 十三山入秋 阅读(...) 评论(...) 编辑 收藏