ResultMap&&鉴别器&&别名

ResultMap:字段和属性名的对应关系

修改数据库列名称

alter table student1 rename column stuno to sno;
alter table student1 rename column stuname to sname;
alter table student1 rename column stuage to sage;
alter table student1 rename column graname to gname;

 字段名->属性名

srcorgmyymapperstudentMapper.xml

    <!--如果字段名和属性名不一致，需要使用resultMap指定对应关系-->
    <select id="queryStudentByStunoWithResultMap" parameterType="int"
            resultMap="studentResultMap">
        select sno,sname,sage,gname from student1 where sno=#{sno}
    </select>
    <resultMap id="studentResultMap" type="student">
        <!--主键-->
        <id column="sno" property="stuNo"/>
        <!--普通字段-->
        <result column="sname" property="stuName"/>
        <result column="sage" property="stuAge"/>
        <result column="gname" property="graName"/>
    </resultMap>

srcorgmyymapperStudentMapper.java

    //stuNo stuName stuAge
    Student queryStudentByStunoWithResultMap(int sno);

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);

        Student student=studentMapper.queryStudentByStunoWithResultMap(1);
        System.out.println(student);

        session.close();

在resultMap中还可以使用鉴别器：对相同sql中不同字段值进行判断，从而进行不同得处理。

srcorgmyymapperstudentMapper.xml

    <select id="queryStudentsWithResultMap"
            resultMap="studentResultMap">
        select sno,sname,nikename,sage,gname from student1
    </select>
    <resultMap id="studentResultMap" type="student">
        <!--主键-->
        <id column="sno" property="stuNo"/>
        <!--普通字段-->
        <!--<result column="sname" property="stuName"/>-->
        <result column="sage" property="stuAge"/>
        <result column="gname" property="graName"/>
        <!--鉴别器:对查询结果进行分支处理，如果是a年级，则真名，如果b年级,显示昵称-->
        <discriminator javaType="String" column="gname">
            <case value="a" resultType="student">
                <result column="sname" property="stuName"/>
            </case>
            <case value="b" resultType="student">
                <result column="nikename" property="stuName"/>
            </case>
        </discriminator>
    </resultMap>

srcorgmyymapperStudentMapper.java

    List<Student> queryStudentsWithResultMap();

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);

        List<Student> students=studentMapper.queryStudentsWithResultMap();
        System.out.println(students);

        session.close();

别名

srcconf.xml

    <typeAliases>
        <!--单个别名(别名忽略大小写)  -->
        <!-- <typeAlias type="org.myy.entity.Student" alias="student"/> -->
        <!--批量定义别名(别名忽略大小写) 以下会自动将该包中的所有类批量定义别名 :别名就是类名（不带包名，忽略大小写） -->
        <package name="org.myy.entity"/>
    </typeAliases>

如果在批量设置别名时，出现了冲突。可以使用@Alias("student")区分

srcorgmyyentityStudent.java

@Alias("student1")
public class Student {