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POHibernate one-to-one entity association with shared PK between 3 classes
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copied!<p>I want a <strong>unidirectional</strong> one-to-one relationship between objects of 3 java classes: Person to Heart, and Person to Liver. I want the objects to share the same PK i.e. every person has a corresponding heart and liver, where person.person_id = heart.heart_id = liver.liver_id. I do not want to merge the 3 tables into 1 because each has loads of fields. Here's my code (mostly based on the accepted answer for <a href="https://stackoverflow.com/questions/787698/jpa-hibernate-one-to-one-relationship">this question</a>):</p> <pre><code>@Entity public class Person { public long personId; private String name; public Heart heart; public Liver liver; // other fields @Id @GeneratedValue public long getPersonId() {return personId;} @OneToOne(cascade = CascadeType.ALL) @PrimaryKeyJoinColumn public Heart getHeart() {return heart;} @OneToOne(cascade = CascadeType.ALL) @PrimaryKeyJoinColumn public Liver getLiver() {return liver;} // other getters and setters and constructors } @Entity public class Heart { private long heartId; private int bpm; private Person person; // other fields @Id @GenericGenerator( name = "generator", strategy = "foreign", parameters = @Parameter(name = "property", value = "person") ) @GeneratedValue(generator = "generator") public long getHeartId() {return heardId;} @OneToOne(mappedBy="heart") @PrimaryKeyJoinColumn public Person getPerson() {return person;} // other getters and setters and constructors } @Entity public class Liver { private long liverId; private boolean healthy; private Person person; // other fields // the rest uses the same hibernate annotation as Heart } </code></pre> <p>I setup the session and do the following:</p> <pre><code>Person jack = new Person(); jack.setName("jack"); Heart heart = new Heart(); heart.setBpm(80); Liver liver = new Liver(); liver.setHealthy(true); </code></pre> <p>Then if I link up the person object with it's organs, and save it, I get an error (NOTE: I got the same behaviour when I just used 2 classes e.g. Person and Heart):</p> <pre><code>jack.setHeart(heart); jack.setLiver(liver); session.save(jack); </code></pre> <blockquote> <p>org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property: person</p> </blockquote> <p>However it works if I set the relationship both ways:</p> <pre><code>jack.setHeart(heart); heart.setPerson(jack); jack.setLiver(liver); liver.setPerson(jack); session.save(jack); </code></pre> <p>But surely this should not be necessary for unidirectional relationships?<br> Cheers </p> <p>ps. Oddly enough, I notice it works (saves both objects to the DB) when I just use 2 classes e.g. Person and Heart, and I just set the link the other way:</p> <pre><code>heart.setPerson(jack); session.save(heart); </code></pre> <p>I have no idea why this works (it seems logical to me that Person is the parent object, as it auto-generates it's own PK, and the others use that; so that's all you should have to setup), but anyway I cannot figure out how to apply this working method to my 3-class situation...</p>

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