MantToMany - Cannot add or update a child row: a foreign key constraint fails

Question

I am trying to create Many to Many relationship and save some data to database. I have entities:

@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class UnifiedOfferEntity {
    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "uuid2")
    private String idOffer;
    private String companyName;
    private String city;
    private String street;
    private String title;
    private LocalDateTime posted;
    private String url;
    private boolean remote;
    private boolean remoteRecruitment;
    @ManyToMany
    @JoinTable(
        name = "terms_of_contract",
        joinColumns = @JoinColumn(name = "offer_id"),
        inverseJoinColumns = @JoinColumn(name = "contract_id"))
    private Set<ContractDetailsEntity> contractDetails = new HashSet<>();
}

@Entity
@Data
@Table(name = "ContractDetails")
@AllArgsConstructor
@NoArgsConstructor
public class ContractDetailsEntity {
    @Id
    @Column(name = "id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private String id;
    @Enumerated(EnumType.STRING)
    private TypeOfContract typeOfContract;
    private double salaryFrom;
    private double salaryTo;
    @ManyToMany(mappedBy = "contractDetails")
    private Set<UnifiedOfferEntity> unifiedOffers = new HashSet<>();

}

And when I want to save something I am getting that execption and I do not know what is wrong:

java.sql.SQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`jobfinder`.`terms_of_contract`, CONSTRAINT `FKfyi46wtjxm9cmb5fh28lf47qt` FOREIGN KEY (`contract_id`) REFERENCES `contract_details` (`id`))

Answer 1

Try to map you entity like this way

  @ManyToMany(cascade = {
        CascadeType.PERSIST,
        CascadeType.MERGE
    })
    @JoinTable(
        name = "terms_of_contract",
        joinColumns = @JoinColumn(name = "offer_id"),
        inverseJoinColumns = @JoinColumn(name = "contract_id"))
    private Set<ContractDetailsEntity> contractDetails = new HashSet<>();