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);

}

}