JPA Repository.findById() returns null but the value is exist on db

Question

I'm developing Spring boot project, using JPA.

What I wanna know is repository.findById(id) method returns null, whereas data is available in the DB.

Functions save() and findAll() are working fine. When I ran the same code on junit test environment, but it completely worked. If the data is hard coded, like memberRepository.findById("M001");, it working fine.

Entity

@Entity
@Table(name="df_member")
public class DfMember {
    
    @Column(name="member_type")
    private String memberType;

    @Id
    @Column(name="id")
    private String id;
    
        ...columns...
        ...Getters/Setters.....

Controller

    @ResponseBody
    @RequestMapping(value="/checkIdDuplicate", method=RequestMethod.POST)
    public boolean checkIdDuplicate(@RequestBody String id) {

       return memberService.isExistByUserId(id);
    }

MemberService

    public boolean isExistByUserId(String id) {
        Optional<DfMember> member = memberRepository.findById(id);
        return member.isPresent();
    }

Repository

public interface MemberRepository extends CrudRepository<DfMember, String> {
    
}

Should return Member Object but it's null.

Answer 1

While the OP has solved his issue, I have to add my answer to the same problem, but with a different cause, because I'm sure will be helpful after hours of debugging I found in the source code of Hibernate (5.4.18) a try/catch that when a EntityNotFoundException is thrown in the hydration process the findBy returns null, even if the entity exists, and it's hydrated successfully. This is because a related referenced entity doesn't exists and Hibernate expect it to exists

For example I have two entities Unit and Improvement where I store an unit with id 5 to have an improvement with id 0 (which doesn't exists), then unitRepository.findById() returns null, instead of the Unit entity with id 5.

@Entity
@Table(name = "units")
public class Unit {
    @ManyToOne(fetch = FetchType.LAZY)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "improvement_id")
    @Cascade({ CascadeType.MERGE, CascadeType.PERSIST, CascadeType.DELETE })
    private Improvement improvement;
}

The reason this happened was because an import script used 0 as value for the improvement_id instead of the original NULL.

Hint: Becareful with disabling Foreign Key checks in import scritps

Best regards