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服务器之家。

原文链接：https://www.jianshu.com/p/1666ac29eb90