JPA-find by 외래키(FK) 조회 방법

기본적인 정보는 JpaRepository를 통해 쉽고 빠르게 처리할 수 있다.
findBy를 사용해서 Entity의 컬럼값으로 조회하는 방법은 알지만 FK의 값으로 조회하고싶은 경우는 어떻게 findBy를 작성해야 되는지 몰라서 글을 작성하게되었다.

package com.example.springProject.entity;

import com.example.springProject.dto.BoardDTO;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

import javax.persistence.*;

@Entity
@Getter
@Setter
@ToString
public class BoardEntity extends BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column
    private String boardWriter;

    @Column
    private String boardTitle;

    @Column(length = 555)
    private String boardContents;

    @Column
    private int boardHits;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "member_id")
    private MemberEntity memberEntity;

    public static BoardEntity toBoardEntity(BoardDTO boardDTO, MemberEntity memberEntity) {
        BoardEntity boardEntity = new BoardEntity();
        boardEntity.setBoardWriter(boardDTO.getBoardWriter());
        boardEntity.setBoardTitle(boardDTO.getBoardTitle());
        boardEntity.setBoardContents(boardDTO.getBoardContents());
        boardEntity.setMemberEntity(memberEntity);
        boardEntity.setBoardHits(0);
        return boardEntity;
    }
}

package com.example.springProject.entity;

import com.example.springProject.dto.MemberDTO;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import org.springframework.web.bind.annotation.GetMapping;

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;

@Entity
@Getter
@Setter
@Table(name = "member_table")
public class MemberEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY) //auto-increment
    private Long memberId;
    @Column(unique = true)
    private String memberEmail;
    @Column
    private String memberPassword;
    @Column
    private String memberName;
    @Column
    private int memberAge;
    @Column(unique = true)
    private String memberPhone;

    @OneToMany(mappedBy = "memberEntity", cascade = CascadeType.REMOVE, orphanRemoval = true, fetch = FetchType.LAZY)
    private List<BoardEntity> boardEntityList = new ArrayList<>();


    public static MemberEntity toMemberEntity(MemberDTO memberDTO) {

        MemberEntity memberEntity = new MemberEntity();
        //memberEntity.setMemberId(memberDTO.getMemberId());
        memberEntity.setMemberEmail(memberDTO.getMemberEmail());
        memberEntity.setMemberPassword(memberDTO.getMemberPassword());
        memberEntity.setMemberName(memberDTO.getMemberName());
        memberEntity.setMemberAge(memberDTO.getMemberAge());
        memberEntity.setMemberPhone(memberDTO.getMemberPhone());
        return memberEntity;
    }

    public static MemberEntity toUpdateMemberEntity(MemberDTO memberDTO) {
        MemberEntity memberEntity = new MemberEntity();
        memberEntity.setMemberId(memberDTO.getMemberId());
        memberEntity.setMemberEmail(memberDTO.getMemberEmail());
        memberEntity.setMemberPassword(memberDTO.getMemberPassword());
        memberEntity.setMemberName(memberDTO.getMemberName());
        memberEntity.setMemberAge(memberDTO.getMemberAge());
        memberEntity.setMemberPhone(memberDTO.getMemberPhone());
        return memberEntity;
    }
}

두개의 Entity중 BoardEntity에서 어떠한 MemberEntity객체와 연결된 정보를 모두 갖고 오고싶을때

findBy+(fk를 관리하는 entity의 필드명에서 첫글자 대문자)+_+(fk를 관리하는 entity의 식별자(PK)필드명에서 첫글자 대문자)

package com.example.springProject.repository;

import com.example.springProject.entity.BoardEntity;
import com.example.springProject.entity.MemberEntity;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface BoardRepository extends JpaRepository<BoardEntity, Long> {
    List<BoardEntity> findByMemberEntity_MemberId(Long id);
}

위와 같이 FK값을 가지고 조회하는 방법입니다!