Mybatis：⼀对多查询

向右看齐 2024-03-23 13:10 33阅读 0赞

### 需求 ###

查询⼀个⽤户，与此同时查询出该⽤户具有的订单

### Bean ###

public class User implements Serializable {
    
        private Integer id;
        private String username;
    
        // 表示用户关联的订单
        private List<Order> orderList = new ArrayList<>();
    }
    
    
    public class Order {
    
        private Integer id;
        private String orderTime;
        private Double total;
    }

### 第一种方式XML ###

#### Mapper ####

public interface IUserMapper {
    
        //查询所有用户、同时查询每个用户关联的订单信息
        public List<User> findAll();
    }

#### XML ####

v    <resultMap id="userMap" type="com.wuxian.pojo.User">
            <result property="id" column="uid"></result>
            <result property="username" column="username"></result>
            <collection property="orderList" ofType="com.wuxian.pojo.Order">
                <result property="id" column="id"></result>
                <result property="orderTime" column="orderTime"></result>
                <result property="total" column="total"></result>
            </collection>
        </resultMap>
    
        <select id="findAll" resultMap="userMap">
            select * from user u left join orders o on u.id = o.uid
        </select>

### 第二种方式注解 ###

#### Mapper ####

public interface IUserMapper {
    
        //查询所有用户、同时查询每个用户关联的订单信息
        @Select("select * from user")
        @Results({
                @Result(property = "id",column = "id"),
                @Result(property = "username",column = "username"),
                @Result(property = "orderList",column = "id",javaType = List.class,
                    many=@Many(select = "com.wuxian.mapper.IOrderMapper.findOrderByUid"))
        })
        public List<User> findAll();
    }
    
    
    
    public interface IOrderMapper {
    
        @Select("select * from orders where uid = #{uid}")
        public List<Order> findOrderByUid(Integer uid);
    }