SpringBoot Data JPA 关联表查询 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.
 */
@Repository
public 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
@Transactional
public 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";
  }
}