如何从外部 id 获取主键以作为外键引用？

Question

So I have a family entity class like this:

@Entity
public class Family {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    @Column(name = "familyName")
    private String familyName;
    @Column(name = "externalID")
    private String externalID;

    public Family(String familyName) {
        this.familyName = familyName;
        this.externalID = UUID.randomUUID().toString();
    }
}

Where I will be getting only family name from FamilyDTO and will be generating the id for internal purposes and for database PK and an externalID to give back to the client.

Now I have a person class:

@Entity
public class Person {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    @Column(name = "name")
    private String name;

    private Integer familyID;    // should be a foreign key to the family primary key id

    public Project(String name) {
        this.name = name;
    }
}

I will be taking name and familyExternalID from PersonDTO :

public class PersonDTO {
    private String name;
    private Integer familyExternalID;
}

Now the thing is I have to use family id as the foreign key and not the familyexternalID (in the person table), So how to map familyExternalID to family id in the family table and then add family id as the foreign key?

Answer 1

It seems you should create a relationship between Family and Person entities:

@Entity
public class Person {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    @Column(name = "name")
    private String name;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "familyID")
    private Family family;

    public Person(String name) {
        this.name = name;
    }
    // getters/setters...

    public String getFamilyExternalID() {
        if (null != this.family) {
            return this.family.getExternalID();
        }
        return null;
    }
}

As for PersonDTO, you'd be able to use family externalID when you build the DTO:

PersonDTO personDTO = new PersonDTO();
personDTO.setName(person.getName());
personDTO.setFamilyExternalID(person.getFamilyExternalID());