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。

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。

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原文地址：https://www.jb51.net/article/143060.htm