mybatis学习之输出映射

resultType

使用resultType进行输出映射，只有查询出来的列名和pojo中的属性名一致，该列才可以映射成功。

如果查询出来的列名和pojo中的属性名全不一致，就没有创建pojo对象

只要查询出来的列名和pojo属性名有一个一致，就会创建pojo对象

输出简单类型

需求：

用户信息的综合查询的列表总数，通过查询总数和上面用户综合查询的列表才可以实现分页

mapper.xml

    
    
        select COUNT(*) from user  where user.sex = #{userCustom.sex} and user.username LIKE '%${userCustom.username}%'
    

mapper.java

    //用户信息总数的查询
    public int findUserCount(UserQueryVo userQueryVo) throws Exception;

测试代码

    @Test
    public void testFindUseCount() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //创建一个UserMapper的对象,mybatis自动生成mapper代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //创建pojo包装对象
        UserQueryVo userQueryVo = new UserQueryVo();
        //创建pojo扩展对象
        UserCustom userCustom = new UserCustom();
        userCustom.setSex("1");
        userCustom.setUsername("测试");
        //将pojo扩展对象set进pojo包装对象
        userQueryVo.setUserCustom(userCustom);
        //调用UserMapper的方法
        int count = userMapper.findUserCount(userQueryVo);
        System.out.println(count);
    }

小结

查询出来的结果集只有一行且一列，可以使用简单类型进行输出映射。

不管输出的pojo对象是单个对象还是一个对象集合，在mapper.xml里面的resultType里，都是指定的对象名称

但是在mapper.java接口类中指定返回值的类型不一样

根据selectOne还是selectList来确定的

resultMap

mybatis中使用resultMap完成高级输出结果映射

使用方法

如果查出来的列名和pojo的属性名不一致，通过定义一个resultMap对列名和pojo属性名之间做一个映射关系。

1、定义resultMap

2、使用resultMap作为statement的输出映射类型

需求；将下面的sql使用UserCustom完成映射

	SELECT id id_,username username_ FROM USER WHERE id = #{id}

可以发现，User类中属性名与上面sql查询的列名并不一致

下面是我们使用resultMap做一个映射的方法：

1.定义resultMap

2.使用resultMap作为输出类型

    
    
        SELECT id id_,username username_ FROM USER WHERE id = #{id}
    

加入接口类方法

    //使用resultMap映射输出结果
    public User findUserByIdResultMap(int id) throws Exception;

3.测试

    @Test
    public void testFindUserByIdResultMap() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //创建一个UserMapper的对象,mybatis自动生成mapper代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //调用UserMapper的方法
        User user = userMapper.findUserByIdResultMap(28);
        System.out.println(user);
    }

4.运行结果

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - Class not found: org.jboss.vfs.VFS
DEBUG [main] - JBoss 6 VFS API is not available in this environment.
DEBUG [main] - Class not found: org.jboss.vfs.VirtualFile
DEBUG [main] - VFS implementation org.apache.ibatis.io.JBoss6VFS is not valid in this environment.
DEBUG [main] - Using VFS adapter org.apache.ibatis.io.DefaultVFS
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo
DEBUG [main] - Reader entry: User.class
DEBUG [main] - Reader entry: UserCustom.class
DEBUG [main] - Reader entry: UserQueryVo.class
DEBUG [main] - Listing file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/User.class
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/User.class
DEBUG [main] - Reader entry: ����   4 L
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/UserCustom.class
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/UserCustom.class
DEBUG [main] - Reader entry: ����   4 
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/UserQueryVo.class
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/pojo/UserQueryVo.class
DEBUG [main] - Reader entry: ����   4 
DEBUG [main] - Checking to see if class pojo.User matches criteria [is assignable to Object]
DEBUG [main] - Checking to see if class pojo.UserCustom matches criteria [is assignable to Object]
DEBUG [main] - Checking to see if class pojo.UserQueryVo matches criteria [is assignable to Object]
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper
DEBUG [main] - Reader entry: UserMapper.class
DEBUG [main] - Reader entry: UserMapper.xml
DEBUG [main] - Listing file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper/UserMapper.class
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper/UserMapper.class
DEBUG [main] - Reader entry: ����   4    findUserByIdResultMap (I)Lpojo/User; 
DEBUG [main] - Find JAR URL: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper/UserMapper.xml
DEBUG [main] - Not a JAR: file:/E:/%e5%a4%a7%e5%ad%a6%e9%a1%b9%e7%9b%ae/IDEA%20Project/mybatis/out/production/mybatis/mapper/UserMapper.xml
DEBUG [main] - Reader entry: 
DEBUG [main] - Checking to see if class mapper.UserMapper matches criteria [is assignable to Object]
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 662736689.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@27808f31]
DEBUG [main] - ==>  Preparing: SELECT id id_,username username_ FROM USER WHERE id = ? 
DEBUG [main] - ==> Parameters: 28(Integer)
DEBUG [main] - <==      Total: 1
User{id=28, username='fjnmbb124', sex='null', birthday=null, address='null'}

Process finished with exit code 0

总结

使用resultType进行输出映射，只有查询出来的列名和pojo中的属性名一致，该列才可以映射成功。

如果查出来的列名和pojo的属性名不一致，通过定义一个resultMap对列名和pojo属性名之间做一个映射关系。