当子实体与父实体之间具有一对一的JPA关系时，可以持久保留子实体和父实体吗？

Question

I am having two Entity classes, Company and CompanyTypeAutomobile .
These two have One-To-One relationships.

public class Company {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    @Column(name = "company_id", unique = true, nullable = false)
    private Integer companyId;

    @Column(name = "name", length = 255, updatable = false)
    @NotEmpty
    private String name;

    private CompanyType companyType;

    //other fields

}

public class CompanyTypeAutomobile {

    @Id
    private Integer id;

    @JsonIgnore
    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    @JoinColumn(name = "company_id")
    private Company company;

}

Company contains the basic details of a company, and the other fields would be contained in its child entity(based on the type of Company) Now, when If Company is created, should I create the CompanyTypeAutomobile also in the same process?

I am having a requirement where I am in such a situation. If for some company, it has only basic details in Company and other details were not created and I want GET the complete details of the company then the persistence layer would return me EntityNotFoundException for CompanyTypeAutomobile .

So I just want to create the child entity, only with the id field. Is it a good practice?

Answer 1

Now, when If Company is created, should I create the CompanyTypeAutomobile also in the same process?

It depends on whether the child entity is mandatory or not.

When you load the child entity using the Company identifier:

CompanyTypeAutomobile details = entityManager.find(CompanyTypeAutomobile.class, company.getId());

you will get null if there is no CompanyTypeAutomobile in the DB, not an EntityNotFoundException .

So I just want to create the child entity, only with the id field. Is it a good practice?

No, it's not. That would be a hack.

If you get an EntityNotFoundException , it means you mapped the child association in the parent entity, which is a mistake .

In that case, remove the CompanyTypeAutomobile association in the parent Company entity as it will behave according to the EAGER fetching strategy and lead to N+1 query issues .