MyBatis注解开发

随着这几年来注解开发越来越流行，Mybatis也可以使用注解开发方式，这样我们就可以减少编写Mapper映射文件了。常用注解有：

注解	说明
@Insert	新增
@Update	更新
@Delete	删除
@Select	查询
@Result	结果集封装
@Results	与@Result 一起使用，封装多个结果集
@One	一对一结果集封装
@Many	一对多结果集封装

简单增删查改

使用注解开发，配置方式与MyBatis简单应用无异，仅是将Mapper映射文件sql的编写转义到了注解中，这里同样以user表为例子，仅展示示例的注解写法，其他配置不作详细说明：

@Select("select * from User")
List<User> findAll();
@Insert("insert into user(username, password) values(#{username}, #{password})")
Integer add(User user);
@Update("update user set username = #{username}, password = #{password} where id = #{id}")
Integer update(User user);
@Delete("delete from user where id= #{id}")
Integer deleteById(Integer id);

测试用例：

public class MyBatisAnnotationTest {

    private UserMapper userMapper;
    private SqlSession sqlSession;

    @Before
    public void before() throws IOException {
        // 加载核⼼配置⽂件
        InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        // 获得sqlSession⼯⼚对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        // 获得sqlSession对象
        sqlSession = sqlSessionFactory.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @After
    public void after() {
        // 释放资源
        sqlSession.close();
    }

    @Test
    public void testSelectAll() {
        // 执⾏sql语句
        List<User> userList = userMapper.findAll();
        // 打印结果
        System.out.println(userList);
    }

    @Test
    public void testAdd() {
        User user = new User();
        user.setUsername("jacky_2");
        user.setPassword("123456");
        // 执⾏sql语句
        int insert = userMapper.add(user);
        System.out.println(insert);
        sqlSession.commit();
    }

    @Test
    public void testUpdate() {
        User user = new User();
        user.setId(4);
        user.setUsername("jacky_2");
        user.setPassword("1234567");
        // 执⾏sql语句
        int update = userMapper.update( user);
        System.out.println(update);
        sqlSession.commit();
    }

    @Test
    public void testDeleted() {
        int delete = userMapper.deleteById(4);
        System.out.println(delete);
        sqlSession.commit();
    }

}

复杂映射开发

除了在映射文件中通过配置来实现复杂映射，我们还可以使用 @Results、@Result、@One、@Many这些注解组合完成复杂关系的配置。

注解	说明
@Results	代替的是标签<resultMap>。该注解中可以使用单个@Result注解，也可以使用@Result集合。使用格式： @Results ( (@Result () [ , @Result () ] ...) )
@Resut	代替了<id>标签和<result>标签 属性介绍： - column：数据库的列名 - property：需要装配的属性名 - one：需要使用的 @One 注解 (@Result (one=@one) ( ) ) - many：需要使用的@Many 注解 (@Result (many=@many) ( ) )
@One（	一对一。代替了<assocation>标签，是多表查询的关键，在注解中用来指定子查询返回单一对象。 属性介绍： - select: 指定用来多表查询的 sql mapper 使用格式：@Result( column=" ", property= ", one=@One(select=""))
@Many	多对一。代替了<collection>标签，是多表查询的关键，在注解中用来指定子查询返回对象集合。 使用格式：@Result(property="",column="", many=@Many (select=""))

这里展示前文Mybatis复杂映射模型改成注解的方式：

一对一

public interface OrderMapper {

    @Select("select * from orders")
    @Results({
            @Result(id=true, property = "id", column = "id"),
            @Result(property = "orderNo",column = "order_no"),
            @Result(property = "amount",column = "amount"),
            @Result(property = "user", column = "uid", javaType = User.class,
                    one = @One(select="org.example.hello.mybatis.mapper.UserMapper.findById"))
    })
    List<Order> findAll();

}

public interface UserMapper {

    @Select("select * from user where id = #{id}")
    User findById(int id);

}

一对多

public interface UserMapper {

    @Select("select * from User")
    @Results({
            @Result(id = true,property = "id", column = "id"),
            @Result(property = "username", column = "username"),
            @Result(property = "password", column = "password"),
            @Result(property = "orderList", column = "id", javaType = List.class,
                    many = @Many(select = "org.example.hello.mybatis.mapper.OrderMapper.findByUid"))
    })
    List<User> findAllWithOrders();

}

public interface OrderMapper {

    @Select("select * from orders where uid = #{uid}")
    List<Order> findByUid(int uid);
  
}

多对多

public interface UserMapper {

    @Select("select * from User")
    @Results({
            @Result(id = true,property = "id", column = "id"),
            @Result(property = "username", column = "username"),
            @Result(property = "password", column = "password"),
            @Result(property = "roleList", column = "id", javaType = List.class,
                    many = @Many(select = "org.example.hello.mybatis.mapper.RoleMapper.findByUid"))
    })
    List<User> findAllWithRoles();

}
public interface RoleMapper {

    @Select("select r.id, r.role_name roleName from role r, user_role ur where r.id = ur.role_id and ur.user_id = #{uid}")
    List<Role> findByUid(int uid);

}