七、mybatis注解实现关联映射(多表联合查询)

1 一对一查询

根据用户ID，查询用户信息，包括用户编号，需要用到tb_user与tb_idcard两张表

分别创建接口 编写查询方法

1.1方式一

package com.yiwu.mapper;
import com.yiwu.pojo.Idcard;
import org.apache.ibatis.annotations.Select;

public interface IdCardMapper {
    @Select("select * from tb_idcard where id = #{id} ;")
    Idcard findIdcardById(int id);    
}

public interface TUserMapper {
    @Select("select * from tb_user where uid = #{uid}")
    @Results(
            @Result(property = "uidcard",
                    column = "ucard_id",
                    one=@One(select = "com.yiwu.mapper.IdCardMapper.findIdcardById"))
    )
    TUser findUserByid(int id);
}

编写测试方法

    @Test
    public void test01(){
        TUser userByid = mapper.findUserByid(1);
        System.out.println(userByid);
    }

1.2 方式二

 @Select("  select u.*,card.id as cardID,card.code as ucard " +
            " from tb_user u,tb_idcard  card \n" +
            " where u.uid = #{uid} and u.ucard_id = card.id")
    @Results({
            @Result(property = "uidcard.id",
                    column = "cardID"

            ),
            @Result(
                    property = "uidcard.code",
                    column = "ucard"
            )
      }
    )

    TUser findUserByid2(int id);

2 一对多查询

根据用户ID，查询用户信息，包括用户编号，需要用到tb_user与tb_order两张表

创建接口

package com.yiwu.mapper;

import com.yiwu.pojo.Order;
import org.apache.ibatis.annotations.Select;
import java.util.List;

public interface OrderMapper {
  @Select("select * from tb_orders where user_id = #{uid} ;")
  List<Order> findUserOrdrsByUid(int uid);
}
}

@Select("select * from tb_user where uid = #{id} ;")
    @Results({
            @Result(
                property = "orderList",
                column ="uid",
            many = @Many(select = "com.yiwu.mapper.OrderMapper.findOrdersByUserId")),

    }

    )
    TUser findUserOrderById(int id);

编写测试方法

@Test
public void test02(){
    TUser userOrderByid = mapper.findUserOrderById(1);
    System.out.println(userOrderByid);
}

3 多对多查询

使用订单表（tb_orders）与商品表（tb_product）借助中间表（tb_ordersitem）

实现多对多查询，根据产品订单，查询该订单所包含的商品。

分别创建接口 编写查询方法

package com.yiwu.mapper;

import com.yiwu.pojo.Product;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface ProductMapper {
    @Select("select *" +
            "from tb_product " +
            "where pd_id in (select pd_id from  tb_ordersitem where or_id = #{orid})")
    List<Product> findProductbyId(int pdId);
}

package com.yiwu.mapper;

import com.yiwu.pojo.Order;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface OrderMapper {
    @Select("select * from tb_orders where user_id = #{id} ;")
    List<Order> findOrdersByUserId(int id);
    @Select("select * from tb_orders where or_id = #{id};")
    @Results(
            @Result(
                    property = "productList",
                    column = "or_id",
                    many = @Many(select = "com.yiwu.mapper.ProductMapper.findProductbyId")
            )
    )
    Order findOrders(int id);
}

编写测试方法

import com.yiwu.mapper.OrderMapper;
import com.yiwu.mapper.TUserMapper;
import com.yiwu.pojo.TUser;
import com.yiwu.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class OrderTest {
    private OrderMapper mapper;
    private SqlSession sqlSession;

    @Before
    public void init(){
    sqlSession = MyBatisUtils.geSqlSession();
    mapper = sqlSession.getMapper(OrderMapper.class);
}
    @Test
    public void test01(){
        mapper.findOrders(1);
    }

    @After
    public void destory(){
        sqlSession.commit();
        sqlSession.close();
    }
}

---

mybatis基础教程【5小时36讲全套】

重录版-推荐（36讲，无法分享组，点击前往bilibili查看全集）

32 注解方式实现一对一查询方式1