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jpa hibernate unidirectional one to one mapping with shared primary key


jpa hibernate unidirectional one to one mapping with shared primary key  using -'java,hibernate,jpa,java-ee,one-to-one'

I'm having a very hard time trying to get a unidirectional one-to-one relationship to work with JPA (Provider: Hibernate). In my opinion this should not be too much of a hassle but apparently JPA / Hibernate disagrees on that ;-)

The problem is that I have to map a legacy schema which I cannot change and that this schema uses a shared primary key between two entities which at the same time is the foreign key for one entity.

I created a simple TestCase:

DB looks as follows:

CREATE TABLE PARENT (PARENT_ID Number primary key, Message varchar2(50));

CREATE TABLE CHILD (CHILD_ID Number primary key, Message varchar2(50),
CONSTRAINT FK_PARENT_ID FOREIGN KEY (CHILD_ID )REFERENCES PARENT (PARENT_ID));

CREATE SEQUENCE SEQ_PK_PARENT START WITH 1 INCREMENT BY 1 ORDER;


The parent(=owning side of one-to-one) looks as follows:

@Entity
@Table(name = "PARENT")
public class Parent implements java.io.Serializable {       
    private Long parentId;
    private String message;
    private Child child;

    @Id
    @Column(name = "PARENT_ID", unique = true, nullable = false, precision = 22, scale = 0)
    @SequenceGenerator(name="pk_sequence", sequenceName="SEQ_PK_PARENT")
    @GeneratedValue(generator="pk_sequence", strategy=GenerationType.SEQUENCE)
    public Long getParentId() {
        return this.parentId;
    }

    public void setParentId(Long parentId) {
        this.parentId = parentId;
    }

    @Column(name = "MESSAGE", length = 50)
    public String getMessage() {
        return this.message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    @OneToOne (cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn(name="PARENT_ID", referencedColumnName="CHILD_ID")
    public Child getTestOneToOneChild() {
        return this.child;
    }

    public void setTestOneToOneChild(Child child) {
        this.child = child;
    }
}


The child:

@Entity
@Table(name = "TEST_ONE_TO_ONE_CHILD", schema = "EXTUSER")
public class Child implements java.io.Serializable {    
    private static final long serialVersionUID = 1L;
    private Long childId;       

    private String message;

    public Child() {
    }

    public Child(String message) {
        this.message = message;
    }

    @Id
    @Column(name = "CHILD_ID")    
    public Long getChildId() {
        return this.childId;
    }

    public void setChildId(Long childId) {
        this.childId = childId;
    }

    @Column(name = "MESSAGE", length = 50)
    public String getMessage() {
        return this.message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}


I totally see the problem that JPA does not know how to assign the id for the child. However I also tried using Hibernates "foreign" key Generator with also no success because that one needs to have a back reference to the parent from child which is not desirable.
This problem does not seem too uncommon to me, so what am I missing here? Is there a solution at all? I can also use hibernate extensions if pure JPA does not provide a solution.

My expectations for a correct behavior would be:
If I try to persist the parent with a child attached:


get ID from sequence, set it on the parent
persist parent
set parent's ID on child
persist child


If I try to persist a "standalone" child (e.g. entityManager.persist(aChild)) I would expect a RuntimeException.

Any help is greatly appreciated!
    
asked Oct 19, 2015 by kinnari
0 votes
9 views



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