MyBatis-03

数据输出：
mapper接口插入 删除 修改时 返回值int就行 只有查询才有resultType

<mapper namespace="com.dc.mapper.EmployeeMapper">
    <delete id="deleteById">
        delete from t_emp where emp_id=#{
   id}
    </delete>

    <select id="queryNameByIdById" resultType="java.lang.String">
        select emp_name from t_emp where emp_id=#{
   id}
    </select>

    <select id="querySalaryById" resultType="java.lang.Double">
        select emp_salary from t_emp where emp_id=#{
   id}
    </select>

    <select id="queryById" resultType="com.dc.pojo.Employee">
        select emp_id empId,emp_name empName,emp_salary empSalary from t_emp where emp_id=#{
   id}
    </select>

    <select id="selectEmpAndMaxSalary" resultType="java.util.Map">
        SELECT
        emp_name 员工姓名,
        emp_salary 员工工资,
        (SELECT AVG(emp_salary) FROM t_emp) 部门平均工资
        FROM t_emp WHERE emp_salary=(
        SELECT MAX(emp_salary)From t_emp
        )
    </select>

        <select id="queryNameBySalary" resultType="java.lang.String">
        select emp_name from t_emp where emp_salary=#{
   salary}
    </select>

    <select id="queryAll" resultType="com.dc.pojo.Employee">
        select emp_id empId,emp_name empName,emp_salary empSalary from t_emp 
    </select>
</mapper>

主键回显

//自增长主键
    <insert id="insertEmp" useGeneratedKeys="true" keyColumn="emp_id" keyProperty="empId">
        insert into t_emp(emp_name,emp_salary) value(#{
   empName},#{
   empSalary})
    </insert>

employee.getEmpId()


//非自增长主键
    <insert id="insertTeacher">
        <selectKey order="BEFORE" resultType="java.lang.String" keyProperty="tId">
            select replace(uuid(),'-','')           //uUId()随机生成,然后去掉-
        </selectKey>
        insert into teacher(t_id,t_name) value(#{
   tId},#{
   tName})
    </insert>

事务自动提交

SqlSession sqlSession = sqlSessionFactory.openSession(true);

列名和属性名不一致
1.select t_id tId,t_name tName from teacher where t_id=#{tId}
2.开启驼峰式映射
3.resultMap自定义映射 （resultType自动映射）

    <resultMap id="tMap" type="com.dc.pojo.Teacher">
        <id column="t_id" property="tId"></id>
        <result column="t_name" property="tName"></result>
    </resultMap>
    <select id="queryById" resultMap="tMap">
        select * from teacher where t_id=#{
   id}
    </select>

原文链接: https://blog.csdn.net/qq_53568730/article/details/135439855