mybatis之关联关系映射（一对多和多对多关系）

今日目标：

1. 一对多关联关系
2. 多对多关联关系

本篇博客是在前四篇的基础上在进行进一步开发的

（四）	mybatis集成ehcache&&mybatis集成redis_m0_58525944的博客-CSDN博客
（三）	mybatis整合spring&&spring整合mybatis分页插件_m0_58525944的博客-CSDN博客
（二）	mybatis之动态sql&&模糊查询&&结果集处理&&mybatis分页&&特殊字符处理_m0_58525944的博客-CSDN博客
（一）	MyBatis入门（逆向生成&&增删改查案例）_m0_58525944的博客-CSDN博客

目录结构：

 准备工作（使用逆向生成工具生成mapper及model）数据库中所需的数据库表，五张表

使用逆向生成工具生成mapper和model

一对多关联关系

利用order和orderitem两个表，来展示一对多的关联关系，一个订单中有多个订单项，多个订单项对应一个订单

1  建立两个vo类来存储一对多的关联属性（OrderVo：订单一方，OrderItemVo：订单项多方）

orderVo

package com.lgs.vo;
import com.lgs.model.Order;
import com.lgs.model.OrderItem;

import java.util.ArrayList;
import java.util.List;

//vo类是为了不破坏本身的类的封装性，跟数据库中的字段一一映射的
public class OrderVo extends Order {
//  一个订单中有多个订单项，所以用集合
    private List orderItems = new ArrayList<>();

    public List getOrderItems() {
        return orderItems;
    }
    public void setOrderItems(List orderItems) {
        this.orderItems = orderItems;
    }
}

OrderItemVo 

package com.lgs.vo;
import com.lgs.model.Order;
import com.lgs.model.OrderItem;

public class OrderItemVo extends OrderItem {
//  一个订单项对应一个订单
    private Order order;

    public Order getOrder() {
        return order;
    }
    public void setOrder(Order order) {
        this.order = order;
    }

}

 2  分别在OrderMapper.xml、OrderItemMapper.xml中添加映射关系配置  和  连表查，所以需要两边都要添加一个dao方法及配置sql语句

OrderMapper.xml

  
  
  
    
    
    
      
      
      
      
    
  

  
  
    select * from t_hibernate_order o,t_hibernate_order_item oi
    where o.order_id = oi.oid
      and o.order_id = #{orderId}
  

OrderItemMapper.xml

  

    
    
    
    
    
      
      
    
  

  
    select * from t_hibernate_order o,t_hibernate_order_item oi
    where o.order_id = oi.oid
      and oi.order_item_id = #{orderItemId}
  

2 OrderMapper.java: 和 OrderItemMapper.java:的配置

OrderMapper.java:

OrderVo queryOrderVoByOrderId(@Param("orderId") Integer orderId);

OrderItemMapper.java:

OrderItemVo queryOrderItemVoByOrderItemId(@Param("orderItemId") Integer orderItemId);

3  建立One2ManyService.java类：

package com.lgs.service;
import com.lgs.vo.OrderItemVo;
import com.lgs.vo.OrderVo;
public interface One2ManyService {
    //通过查询订单关联查询出对应的订单项信息
    OrderVo queryOrderVoByOrderId(Integer orderId);

    //查询订单项，关联查询出所属的订单
    OrderItemVo queryOrderItemVoByOrderItemId(Integer OrderItemId);
}

4  建立One2ManyServiceImpl.java实现类：

package com.lgs.service.impl;
import com.lgs.mapper.OrderItemMapper;
import com.lgs.mapper.OrderMapper;
import com.lgs.service.One2ManyService;
import com.lgs.vo.OrderItemVo;
import com.lgs.vo.OrderVo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class One2ManyServiceImpl implements One2ManyService {

    @Autowired
    private OrderMapper orderMapper;
    @Autowired
    private OrderItemMapper orderItemMapper;
 
    @Override
    public OrderVo queryOrderVoByOrderId(Integer orderId) {
        return orderMapper.queryOrderVoByOrderId(orderId);
    }
    @Override
    public OrderItemVo queryOrderItemVoByOrderItemId(Integer OrderItemId) {
        return orderItemMapper.queryOrderItemVoByOrderItemId(OrderItemId);
    }
}

5  测试

package com.lgs.service.impl;
import com.lgs.model.OrderItem;
import com.lgs.service.One2ManyService;
import com.lgs.vo.OrderItemVo;
import com.lgs.vo.OrderVo;
import junit.framework.TestCase;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"classpath:applicationContext.xml"})
public class One2ManyServiceImplTest extends TestCase {

    @Autowired
    private One2ManyService one2ManyService;
    @Test
    public void queryOrderVoByOrderId() {
        OrderVo orderVo = this.one2ManyService.queryOrderVoByOrderId(10);
        System.out.println(orderVo);
        for (OrderItem orderItem : orderVo.getOrderItems()) {
            System.out.println(orderItem);
        }
    }
    @Test
    public void queryOrderItemVoByOrderItemId() {
        OrderItemVo orderItemVo = this.one2ManyService.queryOrderItemVoByOrderItemId(49);
        System.out.println(orderItemVo);
        System.out.println(orderItemVo.getOrder());
    }

}

 通过查询订单关联查询出对应的订单项信息

查询订单项， 关联所属的订单

多对多关联关系

前面介绍了一对多的关系，那么接下来多对多的映射关系就简单多了，用两个connection配置
为展示多对多的关联关系，利用一本书对应多种类别，一种类别对应多本书的概念

1  建立两个vo类来存储多对多的关联属性（HBookVo：书籍，CategoryVo：书籍种类 都是多方，所以都用集合）

HBookVo.java：

package com.lgs.vo;
import com.lgs.model.Category;
import com.lgs.model.Hbook;
import java.util.ArrayList;
import java.util.List;
public class HbookVo extends Hbook {
    private List categories = new ArrayList<>();

    public List getCategories() {
        return categories;
    }
    public void setCategories(List categories) {
        this.categories = categories;
    }
}

CategoryVo.java:

package com.lgs.vo;
import com.lgs.model.Category;
import com.lgs.model.Hbook;
import java.util.ArrayList;
import java.util.List;
public class CategoryVo extends Category {
    private List hbooks = new ArrayList<>();

    public List getHbooks() {
        return hbooks;
    }
    public void setHbooks(List hbooks) {
        this.hbooks = hbooks;
    }
}

2  在HBookCategoryMapper.xml中添加映射关系配置  和  连表查，所以需要添加一个dao方法及配置sql语句

HBookCategoryMapper.xml（配置两个多对多和连表查的SQL）：

  
    
    
    
      
      
    
  
  
    
    
    
      
      
    
  

  
    select * from t_hibernate_book b,t_hibernate_book_category bc,t_hibernate_category c
    where b.book_id = bc.bid and bc.cid = c.category_id and b.book_id = #{bookId}
  
  
    select * from t_hibernate_book b,t_hibernate_book_category bc,t_hibernate_category c
    where b.book_id = bc.bid and bc.cid = c.category_id and c.category_id=#{cid}
  

3  HBookCategoryMapper.java(添加两个查询方法):

    HbookVo queryByBookId(@Param("bookId") Integer bookId);

    CategoryVo queryByCid(@Param("cid") Integer cid);

4  建立Many2ManyService.java类：

package com.lgs.service;
import com.lgs.vo.CategoryVo;
import com.lgs.vo.HbookVo;
import org.apache.ibatis.annotations.Param;
public interface Many2ManyService {
    HbookVo queryByBookId(Integer bookId);

    CategoryVo queryByCid(Integer cid);
}

5  建立Many2ManyServiceImpl.java实现类：

package com.lgs.service.impl;

import com.lgs.mapper.HbookCategoryMapper;
import com.lgs.service.Many2ManyService;
import com.lgs.vo.CategoryVo;
import com.lgs.vo.HbookVo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class Many2ManyServiceImpl implements Many2ManyService {

    @Autowired
    private HbookCategoryMapper hbookCategoryMapper;

    @Override
    public HbookVo queryByBookId(Integer bookId) {
        return hbookCategoryMapper.queryByBookId(bookId);
    }
    @Override
    public CategoryVo queryByCid(Integer cid) {
        return hbookCategoryMapper.queryByCid(cid);
    }

}

6  测试

package com.lgs.service.impl;
import com.lgs.model.Category;
import com.lgs.model.Hbook;
import com.lgs.service.Many2ManyService;
import com.lgs.vo.CategoryVo;
import com.lgs.vo.HbookVo;
import junit.framework.TestCase;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"classpath:applicationContext.xml"})
public class Many2ManyServiceImplTest extends TestCase {
    @Autowired
    private Many2ManyService many2ManyService;

    @Test
    public void queryByBookId() {
        HbookVo hbookVo = many2ManyService.queryByBookId(8);
        System.out.println(hbookVo);
        for (Category category : hbookVo.getCategories()) {
            System.out.println(category);
        }
    }
    @Test
    public void queryByCid() {
        CategoryVo categoryVo = many2ManyService.queryByCid(8);
        System.out.println(categoryVo);
        for (Hbook hbook : categoryVo.getHbooks()) {
            System.out.println(hbook);
        }
    }
}

根据书的id查看书有哪些类别

根据类别查询此书类别的书还有哪些

 OK！到这就结束了，希望能帮到你！！！