SpringBoot Data JPA 关联表查询的方法

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；}

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；}

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);}

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);  }}

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";  }}