Mybatis注解——一对多

1、数据库建表语句

CREATE TABLE `user` (
  `id` int(11) DEFAULT NULL,
  `username` varchar(50) DEFAULT NULL
);


CREATE TABLE `orderinfo` (
  `id` int(11) DEFAULT NULL,
  `ordertime` datetime DEFAULT NULL,
  `total` decimal(8,2) DEFAULT NULL,
  `uid` int(11) DEFAULT NULL
);

2、实体

public class UserInfo {

    private Integer id;

    private String username;

    private List<OrderInfo> orderInfoList;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public List<OrderInfo> getOrderInfoList() {
        return orderInfoList;
    }

    public void setOrderInfoList(List<OrderInfo> orderInfoList) {
        this.orderInfoList = orderInfoList;
    }

    @Override
    public String toString() {
        return "UserInfo{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", orderInfoList=" + orderInfoList +
                '}';
    }
}

public class OrderInfo {

    private Integer id;

    private Date ordertime;

    private Double total;

    private Integer uid;

    private UserInfo user;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Date getOrdertime() {
        return ordertime;
    }

    public void setOrdertime(Date ordertime) {
        this.ordertime = ordertime;
    }

    public Double getTotal() {
        return total;
    }

    public void setTotal(Double total) {
        this.total = total;
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public UserInfo getUser() {
        return user;
    }

    public void setUser(UserInfo user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "OrderInfo{" +
                "id=" + id +
                ", ordertime=" + ordertime +
                ", total=" + total +
                ", uid=" + uid +
                ", user=" + user +
                '}';
    }
}

3、Mapper 接口java代码

public interface UserMapper {

    @Select("select * from user")
    @Results({
            @Result(property = "id",column = "id"),
            @Result(property = "username",column = "username"),
            @Result(property = "orderInfoList",column = "id",javaType = List.class,
            many = @Many(select = "com.deppon.mapper.OrderMapper.findOrderListByUid"))
    })
    public List<UserInfo> findAll();
}

public interface OrderMapper {

    @Results({
            @Result(property = "id",column = "id"),
            @Result(property = "ordertime",column="ordertime"),
            @Result(property = "total",column="total"),
            @Result(property = "user",column = "uid",javaType = UserInfo.class,
                    one = @One(select = "com.deppon.mapper.UserMapper.findUserById"))
    })

    @Select("select * from orderinfo where uid = #{id}")
    List<OrderInfo> findOrderListByUid(Integer id);

}

4、测试类

public class TestOrderMapperUtil {

    private OrderMapper orderMapper;

    private UserMapper userMapper;

    @Before
    public void before() throws IOException {
        String path = "SqlConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(path);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession(true);
        orderMapper = session.getMapper(OrderMapper.class);
        userMapper = session.getMapper(UserMapper.class);
    }


    @Test
    public void test(){
        List<UserInfo> userInfoList = userMapper.findAll();
        for(UserInfo userInfo:userInfoList){
            System.out.println(userInfo);
        }
    }
}

### MyBatis 注解开发中 resultMap 的使用 在MyBatis注解开发模式下,`@Results` 和 `@Result` 组合用于定义内联的结果映射规则。这种方式允许开发者直接在接口方法上声明映射逻辑而不需要额外的XML配置文件[^1]。 对于较为复杂的映射需求,可以利用这些注解来创建类似于XML风格下的`<resultMap>`标签的功能。下面是一个具体的例子展示如何实现这一点: #### 定义实体类 假设存在两个实体类:`UserDO`表示用户基本信息;另一个是用户的兴趣爱好列表`HobbyDO`。这两个类之间存在着一对的关系。 ```java // UserDO.java public class UserDO { private Integer id; private String name; // getters and setters... } // HobbyDO.java public class HobbyDO { private Integer userId; private String hobbyName; // getters and setters... } ``` #### 创建 Mapper 接口并应用注解 接下来是在Mapper接口里边定义相应的查询方法以及其对应的`resultMap`: ```java package my.springboot.mybatis.dao; import java.util.List; import org.apache.ibatis.annotations.*; import my.springboot.mybatis.entity.HobbyDO; import my.springboot.mybatis.entity.UserDO; @Mapper public interface UserInfoMapper { @Select("SELECT * FROM users WHERE id = #{id}") @Results(id="userResult", value={ @Result(property="id", column="id"), @Result(property="name", column="username") }) UserDO getUserById(@Param("id") int id); @Select("<script>" + "SELECT h.* FROM hobbies h" + "<where>" + "<if test='userId != null'>" + "AND h.user_id = #{userId}" + "</if>" + "</where>" + "</script>") @Results(id="hobbiesResult", value={ @Result(property="userId", column="user_id"), @Result(property="hobbyName", column="hobby_name") }) List<HobbyDO> findHobbiesByUserId(@Param("userId") Integer userId); // 更加复杂的一对关联映射 @Select("SELECT u.*, GROUP_CONCAT(h.hobby_name SEPARATOR ',') AS hobbies " + "FROM users u LEFT JOIN hobbies h ON u.id=h.user_id " + "WHERE u.id=#{id} GROUP BY u.id") @Results({ @Result(id=true, property="id", column="id"), @Result(property="name", column="username"), @Result(property="hobbies", column="hobbies", many=@Many(select="findHobbiesByUserId")) }) UserWithHobbiesDTO getUserWithHobbies(int id); } ``` 在这个例子中,首先为每一个单独的对象(`UserDO`, `HobbyDO`)指定了基本字段之间的映射关系。之后,在最后一个方法`getUserWithHobbies()`展示了更高级别的用法——它不仅获取了一个用户的信息还连带取回了该用户的全部兴趣爱好记录,并通过`many`属性指定子查询的方式完成了一对关系的加载[^4]。
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