SpringBoot Data JPA 关联表查询的方法

SpringBoot Data JPA实现 一对多、多对一关联表查询

开发环境

1. IDEA 2017.1

2. Java1.8

3. SpringBoot 2.0

4. MySQL 5.X

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。

来源：https://www.jianshu.com/p/1666ac29eb90