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.
*/
@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);
}
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
@Transactional
public 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。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
