增加null&&使用HashMap存储查询结果集

增加null

oracle：如果插入的字段是Null，提示错误:Other而不是null

mysql：如果插入的字段是Null，正常执行(没有约束)

原因：各个数据库在mybatis中对各种数据类型的默认值不一致

　　mybatis中，jdbcTypeForNull(如果是null)，则默认值是Other。

　　Other来说，Mysql能够处理（NULL），但是Oracle不行

解决：

　　Oracle：null->Other,需要手工告诉Oracle：other为null

　　a.修改具体的sql标签

当某个数据类型oracle无法处理时，告诉它默认值null

注意此时设置的#{stuName,jdbcType=NULL}不会影响正常的赋值

srcorgmyymapperstudentMapper.xml

    <insert id="addStudent" parameterType="Student" databaseId="oracle">
        <selectKey keyProperty="stuNo" resultType="Integer" order="AFTER">
            select myseq.currval from dual
        </selectKey>
        insert into student1(stuno,stuname,stuage,graname)
        values(myseq.nextval,#{stuName,jdbcType=NULL},#{stuAge},#{graName})
    </insert>

　　b.配置mybatis全局配置文件conf.xml（推荐）

srcconf.xml

 <settings>
        <setting name="jdbcTypeForNull" value="NULL"/>
 </settings>

返回值为HashMap的情况

 srcorgmyymapperstudentMapper.xml

    <select id="queryStudentOutByHashMap" parameterType="int"
            resultType="HashMap">
        select stuNo "no",stuName "name",stuAge "age"
        from  student1 where stuNo=#{stuNo}
    </select>

 其中stuNo是数据库的字段名

"no"是stuNo的别名，用于在map中get值时使用（作为map的key）map.get("no")

如果不加别名，map的key就是字段名

 srcorgmyymapperStudentMapper.java

HashMap<String,Object> queryStudentOutByHashMap(int stuNo);

srcorgmyy estTest.java

        //Connection - SqlSession操作Mybatis
        //conf.xml->reader
        Reader reader = Resources.getResourceAsReader("conf.xml");
        //reader->sqlSession

        //可以通过build的第二参数 指定数据库环境
        SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(reader,"devOracle");
        SqlSession session = sessionFactory.openSession();

        StudentMapper studentMapper=session.getMapper(StudentMapper.class);

        HashMap<String, Object> studentMap = studentMapper.queryStudentOutByHashMap(1);
        System.out.println(studentMap.get("no")+","+studentMap.get("name")+","+studentMap.get("age"));
        System.out.println(studentMap);
        session.close();

key:id　　value:Student

srcorgmyymapperstudentMapper.xml

    <select id="queryStudentsByHashMap"
            resultType="HashMap">
        select stuNo,stuName,stuAge from student1
    </select>

 srcorgmyymapperStudentMapper.java

    //程序根据select的返回值,知道map的value就是Student，根据@MapKey("STUNO")知道map的key是stuNo

　　@MapKey("STUNO")//Oracle的元数据(表名、字段名)都是大写
　　HashMap<Integer,Student> queryStudentsByHashMap();

srcorgmyy estTest.java

        //Connection - SqlSession操作Mybatis
        //conf.xml->reader
        Reader reader = Resources.getResourceAsReader("conf.xml");
        //reader->sqlSession

        //可以通过build的第二参数 指定数据库环境
        SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(reader,"devOracle");
        SqlSession session = sessionFactory.openSession();

        StudentMapper studentMapper=session.getMapper(StudentMapper.class);

        HashMap<Integer, Student> studentsMap = studentMapper.queryStudentsByHashMap();
        //System.out.println(studentMap.get("no")+","+studentMap.get("name")+","+studentMap.get("age"));
        System.out.println(studentsMap);

        session.close();