Fetching specific columns from multiple joined tables in Spring Data JPA

Question

my company recently decided to switch to using Spring Data JPA instead of Mybatis for new projects, so I am pretty new to using Spring Data JPA in general.

I am trying to execute the following sql query

SELECT ab.status, buyer_rate, buyer_name, buyer_tel, bid_price, ADDTIME(complete_dt,"23:00:0.000000") AS send_time, brand, model 
FROM auction_bid ab 
INNER JOIN goods_auction ga ON ab.goods_auction_idx=ga.idx 
INNER JOIN auction_info ai ON ga.auction_info_idx=ai.idx 
WHERE is_success=1 and ab.status='008';

I have created 3 entities each corresponding to the table in my mariadb database

@Entity
@Getter
@Setter
@ToString
public class AuctionBid {
    @Id
    @Column(name = "auction_bid_idx")
    private Long idx;
    @Column
    private Long userIdx;
    @Column
    private String status;
    @Column
    private Long bidPrice;
    @Column
    private int isSuccess;
    @Column
    private int rank;
    @Column
    private Date createdAt;
    @Column
    private Date updatedAt;
    @ManyToOne(fetch = LAZY)
    @JoinColumn(name="goods_auction_idx")
    private GoodsAuction goodsAuction;
}

@Entity
@Getter
@Setter
public class AuctionInfo {
    @Id
    @Column(name = "auction_info_idx")
    private Long idx;
    @Column
    private Long goodsIdx;
    @Column
    private String brand;
    @Column
    private String model;
    @Column
    private String pattern;
    @Column
    private String size;
    @Column
    private String color;
    @Column
    private String tag1;
    @Column
    private String tag2;
    @Column
    private String tag3;
    @Column
    private String comment;
    @Column
    private String korName;
    @Column
    private String oColor;
    @Column
    private String iColor;
    @Column
    private String hColor;
    @Column
    private String oMaterial;
    @Column
    private String iMaterial;
    @Column
    private String origin;
    @Column
    private String realSize;
    @Column
    private Long minBid;
    @Column
    private Double sellerRate;
    @Column
    private Double buyerRate;
    @Column
    private Date createdAt;
    @Column
    private Date updatedAt;
}

@Entity
@ToString
@Getter
@Setter
public class GoodsAuction {
    @Id
    @Column(name = "goods_auction_idx")
    private Long idx;
    @Column
    private String auctionUid;
    @Column
    private String status;
    @Column
    private Date startDt;
    @Column
    private Date finishDt;
    @Column
    private Long step;
    @Column
    private int isReadyActive;
    @Column
    private int isFinishActive;
    @Column
    private int isRecommended;
    @Column
    private String invoice;
    @Column
    private String buyerName;
    @Column
    private String buyerTel;
    @Column
    private String buyerAddr1;
    @Column
    private String buyerAddr2;
    @Column
    private String buyerZipcode;
    @Column
    private Date completeDt;
    @Column
    private Date deliveryDt;
    @Column
    private Long returnTaxPrice;
    @Column
    private String returnInvoice;
    @Column
    private Date returnReqDt;
    @Column
    private Date returnCompDt;
    @Column
    private Date createdAt;
    @Column
    private Date updatedAt;
    @ManyToOne(fetch = LAZY)
    @JoinColumn(name="auction_info_idx")
    private AuctionInfo auctionInfo;
}

And I am trying to map the info that I got from the query to the following object

public class MessageData {
    private String status;
    private Double buyerRate;
    private String buyerName;
    private String buyerTel;
    private Long bidPrice;
    private Date sendTime;
    private String brand;
    private String model;
}

I get that I have to make and interface that extends JpaRepository, but the examples that I have seen seems to just fetch the entire table instead of a select few columns, and I am a little bit confused on how I will be able to map the result to List.

Any feedback will be deeply appreciated!

Thank you in advance!!

Answer 1

You can hql joins instead of inner joins through entity models. like that;

select a from auction_bid ab join ab.goodsAuction gA join auctionInfo aI

You can use 'Data Transfer Objects (DTO)' for fetch specific columns.

Answer 2

For projections, you can try a "select new". I assume the MessageData is in package com.foo :

select new com.foo.MessageData(ab.status, buyer_rate, buyer_name, buyer_tel, bid_price, ADDTIME(complete_dt,"23:00:0.000000"), brand, model) FROM ...