[jeeplus] 使用笔记 (gridSelect、datetimepicker etc.)

慎用 select *

当自己手写一些 sql 时，如果查找的对象/表中有封装了其他对象，那么，当 sql 中有 select * 时会导致封装对象为 Null 的现象。
因此，如果有会使用到封装的对象，那么 xml 中的 sql 还是加上映射关系吧。
eg:

    <!-- 根据年份、省份、高校、文理科、批次查找记录 findListByYPNWB -->
    <select id="findListByYPNWB" resultType="Eucode" >
        SELECT
        <include refid="EucodeColumns"/>
        FROM e_uecode a
        <include refid="EucodeJoins"/>
        WHERE a.year = #{year} AND a.province = #{province.id} AND a.universityid = #{university.id} AND a.wltype = #{wltype} AND a.schoolbatches = #{schoolBatches} AND (a.r3 != "2" OR  ISNULL(a.r3)) AND (a.r3 != "3"  OR  ISNULL(a.r3))
    </select>

java.sql.SQLException: Connection is read-only. Queries leading to data modification are not allowed

解决方法：事务配置在 service 层，但是你的 service 层的方法是 query 开头的，service 调用的 query 方法根本就没有事务。你的配置文件下面是不是还有关于 query*的配置成了 read-only？修改你 service 方法的开头变成不是 read-only 的那种配置，如 clear 开头。（在 query 方法名(read_only)里面执行了 update 操作，所以就报错了。）

    //删除转化出现异常时已经插入的数据记录
    @Transactional(readOnly = false)
    public void deleteERecord(LevelForMajors levelForMajors){
        mapper.deleteERecord(levelForMajors);
    }

SSM 中 MyBatis 的某个 xxxMapper.xml 中，是否可以这样写？

            <if test="planMajorName != null and  planMajorName != '' and r1 = '0'">
                AND a.planmajorname = #{planMajorName}
            </if>
            <if test="planMajorName != null and  planMajorName != '' and (r1 = null or r1 = '')">
                AND a.planmajorname LIKE
                <if test="dbName == 'oracle'">'%'||#{planMajorName}||'%'</if>
                <if test="dbName == 'mssql'">'%'+#{planMajorName}+'%'</if>
                <if test="dbName == 'mysql'">concat('%',#{planMajorName},'%')</if>
            </if>

MySql 中根据 判断某个字段（字符串）的长度后 按不同情况更新 同一个字段的值 的方法：

UPDATE m_levelformajor 

SET type = (
	CASE
		WHEN 1 < LENGTH(number) AND  LENGTH(number) < 3 THEN "2"
		WHEN 3 < LENGTH(number) AND  LENGTH(number) < 5 THEN "3"
		WHEN 6 <= LENGTH(number) THEN "4"
		WHEN number IS NULL THEN "1"
	ELSE
		"1"
	END
)

UPDATE m_levelformajor 
SET type = (
	CASE

		WHEN number IS NULL THEN "1"
	ELSE
		 "1"
	END
)

SELECT id,name, number, type, parent_id,parent_ids , LENGTH(number) FROM m_levelformajor
SELECT id,name, number, type, parent_id,parent_ids , LENGTH(number) FROM m_levelformajor WHERE  LENGTH(number) <5 AND  LENGTH(number) > 3
SELECT id,name, number, type, parent_id,parent_ids , LENGTH(number) FROM m_levelformajor WHERE  1 < LENGTH(number)  AND  LENGTH(number) <3
SELECT id,name, number, type, parent_id,parent_ids , LENGTH(number) FROM m_levelformajor WHERE   LENGTH(number) <1```