mybatis之关联关系映射（一对多和多对多关系）

今日目标：

一对多关联关系

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

        <table schema="" tableName="t_hibernate_order" domainObjectName="Order"enableCountByExample="false" enableDeleteByExample="false"enableSelectByExample="false" enableUpdateByExample="false"></table><table schema="" tableName="t_hibernate_order_item" domainObjectName="OrderItem"enableCountByExample="false" enableDeleteByExample="false"enableSelectByExample="false" enableUpdateByExample="false"></table><table schema="" tableName="t_hibernate_book" domainObjectName="Hbook"enableCountByExample="false" enableDeleteByExample="false"enableSelectByExample="false" enableUpdateByExample="false"></table><table schema="" tableName="t_hibernate_category" domainObjectName="Category"enableCountByExample="false" enableDeleteByExample="false"enableSelectByExample="false" enableUpdateByExample="false"></table><table schema="" tableName="t_hibernate_book_category" domainObjectName="HbookCategory"enableCountByExample="false" enableDeleteByExample="false"enableSelectByExample="false" enableUpdateByExample="false"></table>

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<OrderItem> orderItems = new ArrayList<>();public List<OrderItem> getOrderItems() {return orderItems;}public void setOrderItems(List<OrderItem> 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

  <!--映射--><!--property：实体类的属性 column：表字段--><resultMap id="OrderVoMap" type="com.lgs.vo.OrderVo" ><result property="orderId" column="order_id"></result><result property="orderNo" column="order_no"></result><collection property="orderItems" ofType="com.lgs.model.OrderItem"><result property="orderItemId" column="order_item_id"/><result property="oid" column="oid"></result><result property="productId" column="product_id"></result><result property="quantity" column="quantity"></result></collection></resultMap><!--查询语句--><select id="queryOrderVoByOrderId" resultMap="OrderVoMap" parameterType="java.lang.Integer">select * from t_hibernate_order o,t_hibernate_order_item oiwhere o.order_id = oi.oidand o.order_id = #{orderId}</select>

OrderItemMapper.xml

<!--多方的配置-->
<resultMap id="OrderVoMap" type="com.lgs.vo.OrderItemVo" ><result property="orderItemId" column="order_item_id"></result><result property="oid" column="oid"></result><result property="productId" column="product_id"></result><result property="quantity" column="quantity"></result><association property="order" javaType="com.lgs.model.Order"><result property="orderId" column="order_id"></result><result property="orderNo" column="order_no"></result></association></resultMap><select id="queryOrderItemVoByOrderItemId" resultMap="OrderVoMap" parameterType="java.lang.Integer">select * from t_hibernate_order o,t_hibernate_order_item oiwhere o.order_id = oi.oidand oi.order_item_id = #{orderItemId}</select>

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 {@Autowiredprivate OrderMapper orderMapper;@Autowiredprivate OrderItemMapper orderItemMapper;@Overridepublic OrderVo queryOrderVoByOrderId(Integer orderId) {return orderMapper.queryOrderVoByOrderId(orderId);}@Overridepublic 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 {@Autowiredprivate One2ManyService one2ManyService;@Testpublic void queryOrderVoByOrderId() {OrderVo orderVo = this.one2ManyService.queryOrderVoByOrderId(10);System.out.println(orderVo);for (OrderItem orderItem : orderVo.getOrderItems()) {System.out.println(orderItem);}}@Testpublic 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<Category> categories = new ArrayList<>();public List<Category> getCategories() {return categories;}public void setCategories(List<Category> 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<Hbook> hbooks = new ArrayList<>();public List<Hbook> getHbooks() {return hbooks;}public void setHbooks(List<Hbook> 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）：

  <resultMap id="HbookVoMap" type="com.lgs.vo.HbookVo"><result property="bookId" column="book_id"></result><result property="bookName" column="book_name"></result><collection property="categories" ofType="com.lgs.model.Category"><result property="categoryId" column="category_id"></result><result property="categoryName" column="category_name"></result></collection></resultMap><resultMap id="CategoryVoMap" type="com.lgs.vo.CategoryVo"><result property="categoryId" column="category_id"></result><result property="categoryName" column="category_name"></result><collection property="hbooks" ofType="com.lgs.model.Hbook"><result property="bookId" column="book_id"></result><result property="bookName" column="book_name"></result></collection></resultMap><select id="queryByBookId" resultMap="HbookVoMap" parameterType="java.lang.Integer">select * from t_hibernate_book b,t_hibernate_book_category bc,t_hibernate_category cwhere b.book_id = bc.bid and bc.cid = c.category_id and b.book_id = #{bookId}</select><select id="queryByCid" resultMap="CategoryVoMap" parameterType="java.lang.Integer">select * from t_hibernate_book b,t_hibernate_book_category bc,t_hibernate_category cwhere b.book_id = bc.bid and bc.cid = c.category_id and c.category_id=#{cid}</select>

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 {@Autowiredprivate HbookCategoryMapper hbookCategoryMapper;@Overridepublic HbookVo queryByBookId(Integer bookId) {return hbookCategoryMapper.queryByBookId(bookId);}@Overridepublic 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 {@Autowiredprivate Many2ManyService many2ManyService;@Testpublic void queryByBookId() {HbookVo hbookVo = many2ManyService.queryByBookId(8);System.out.println(hbookVo);for (Category category : hbookVo.getCategories()) {System.out.println(category);}}@Testpublic 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！！！