SpringBoot Data JPA实现 一对多、多对一关联表查询
开发环境
功能需求
通过关联关系查询商店Store中所有的商品Shop，商店对商品一对多，商品对商店多对一,外键 store_id存在于多的一方。使用数据库的内连接语句。
表结构
tb_shop
tb_store
实体类，通过注解实现
1.商店类Store.java
package com.gaolei.Entity;import javax.persistence.*;import java.util.HashSet;import java.util.Set;/** * Created by GaoLei on 2018/6/25. */@Entity@Table(name = "tb_store")public class Store { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Integer id;//商铺号 private String name;//商铺姓名 private String address;//商铺地址 private int tel ;//商铺联系 private String info;//商铺信息 @OneToMany(cascade = CascadeType.ALL,mappedBy = "store") private Set<Shop> shops = new HashSet<Shop>(); // 省略set()和get()方法；}商品类Shop.java
package com.gaolei.Entity;import javax.persistence.*;import java.util.HashSet;import java.util.Set;/** * Created by GaoLei on 2018/6/25. */@Entity@Table(name = "tb_shop")public class Shop { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Integer id ; //商品id private String name;//商品名 private int price;// 商品价格 private int num;//商品数量 private String info;//商品信息 @ManyToOne @JoinColumn(name = "store_id")//外键 private Store store; // 省略set()和get()方法；}StoreDao.java
CrudRepository 接口继承于 Repository 接口，并新增了简单的增、删、查等方法。其中封装好了很多的方法，这里不再概述，自行百度，这里通过自定义HQL语句完成复杂的操作。
package com.gaolei.Dao;import com.gaolei.Entity.Store;import org.springframework.data.jpa.repository.Query;import org.springframework.data.repository.CrudRepository;import org.springframework.stereotype.Repository;import java.util.List;/** * Created by GaoLei on 2018/6/25. */@Repositorypublic interface StoreDao extends CrudRepository<Store,Integer> { //此方法通过内连接查询店铺id=?中的所有商品 @Query("select distinct s from Store s inner join s.shops where s.id = ?1") List<Store> findByShopList(Integer id);}StoreService.java
通过@Autowired注入StoreDao来实现方法
package com.gaolei.Service;import com.gaolei.Dao.StoreDao;import com.gaolei.Entity.Shop;import com.gaolei.Entity.Store;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;import org.springframework.transaction.annotation.Transactional;import java.util.List;/** * Created by GaoLei on 2018/6/25. */@Controller@Transactionalpublic class StoreService { @Autowired private StoreDao storeDao; /** * 展示商店商品 * */ public List<Store> findByShopList(Integer id){ return storeDao.findByShopList(id); }}StoreAction.java
实现具体数据操作操作
package com.gaolei.Action;import com.gaolei.Entity.Shop;import com.gaolei.Entity.Store;import com.gaolei.Service.ShopService;import com.gaolei.Service.StoreService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.web.bind.annotation.RequestMapping;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.util.ArrayList;import java.util.List;/** * Created by GaoLei on 2018/6/26. */@Controller@RequestMapping("/store")public class StoreAction { @Autowired private StoreService storeService; /** * Store_shop_menu展示店铺商品 * */ @RequestMapping("showShop") public String showShop(HttpServletResponse response ,HttpServletRequest request,Model model){ String id = request.getParameter("store_id"); //通过HQL语句拿到id=?的商铺，并拿到该店铺下所有的商品 List<Store> list = storeService.findByShopList(Integer.valueOf(id)); //返回的为一个Store集合，Store类和Shop类为一对多，Store下的shops为List<Shop>。 List<Shop> shopList = new ArrayList<Shop>();//循环遍历拿到每一个shop,添加到一个新的List<Shop>中，用于将数据在前台展示。 for (Store store:list){ System.out.println(store.getName()); for (Shop shop: store.getShops()) { System.out.println(shop.getName()); shopList.add(shop); } } model.addAttribute("list",shopList); return "admin/showShop"; }}前台页面跳转
查看的店铺
店铺商品
省略前端代码，主要的是@Query("****************")中语句使用，配合数据库的各种连接能实现复杂的操作。
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