mybatis之动态SQL操作之更新

1）  更新条件不确定，需要根据情况产生SQL语法，这种情况叫动态SQL

/**
 * 持久层*/
public class StudentDao {
    /**
     * 动态SQL--更新
     */
    public void dynaSQLwithUpdate(Student student) throws Exception{
        SqlSession sqlSession = MyBatisUtil.getSqlSession();
        try{
            sqlSession.update("mynamespace.dynaSQLwithUpdate",student);
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
            MyBatisUtil.closeSqlSession();
        }
    }
    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        dao.dynaSQLwithUpdate(new Student(10,null,5000D));
        dao.dynaSQLwithUpdate(new Student(10,"哈哈",null));
        dao.dynaSQLwithUpdate(new Student(10,"哈哈",6000D));
    }
}

<?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="mynamespace">
    <update id="dynaSQLwithUpdate" parameterType="loaderman.Student">
        update students 
        <set>
            <if test="name!=null">
                name=#{name},
            </if>
            <if test="sal!=null">
                sal=#{sal},
            </if>
        </set>
        where id=#{id}
    </update>    
</mapper>