Hibernate @ManyToOne Class reference using @NaturalId instead of @Id

Question

I have Hibernate / JPA annotations (still don't know what the difference is, to be honest) that allow me to create an association class. This class combines two elements that are associated with one object. I originally used @JoinTable , but realized that I needed a lot more metadata with associations, so I had to convert the code to a different type of object.

I am currently using @Id to mark the ID column for my objects and using @NaturalId (mutable = false) for String uuid .

My association class uses @ManyToOne and creates the table just fine, but when I look at it, the table uses the @Id field as the display column. I would prefer this association class to use @NaturalId uuid for the convenience of transferring relationships / associations to other systems.

How can I get the relation to use the correct identifier?

For reference, my DB and Java code is as follows:

 AssociationsTable ---------------------------------------------- | ID | META DATA | ID ASSOC. 1 | ID ASSOC. 2 | ---------------------------------------------- | 1 | stuff | 1 | 2 | ---------------------------------------------- Objects ------------------------------ | ID | META DATA | UUID | ------------------------------ | 1 | stuff | FOO-123 | ------------------------------ | 2 | stuff | BAR-456 | ------------------------------ Association Class{ ObjA main; ObjA sub; @ManyToOne getMain() @ManyToOne getSub() } ObjA Class{ Long id; @Id @GeneratedValue(generator="increment") @GenericGenerator(name="increment", strategy = "increment") @XmlElement @Column(name = "ID", unique = true, nullable = false) getId() String uuid; @NaturalId (mutable = false) @GeneratedValue(generator = "uuid") @GenericGenerator(name = "uuid", strategy = "uuid2") @Column(name = "uuid", unique = true) getUUID() } 

Answer 1

You can use the referencedColumnName @JoinColumn attribute as indicated here . Therefore, for your example, the mappings should be as follows:

ObjA.java:

 package hello; import org.hibernate.annotations.NaturalId; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; @Entity public class ObjA { Long id; String uuid; public ObjA() { } public ObjA(String uuid) { this.uuid = uuid; } @Id @GeneratedValue @Column(name = "obj_a_id", unique = true, nullable = false) Long getId() { return id; } public void setId(Long id) { this.id = id; } @NaturalId(mutable = false) @Column(name = "uuid", unique = true, nullable = false) public String getUuid() { return uuid; } public void setUuid(String uuid) { this.uuid = uuid; } } 

Association.java:

 package hello; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; @Entity public class Association { Long id; ObjA main; ObjA sub; public Association() { } public Association(ObjA main, ObjA sub) { this.main = main; this.sub = sub; } @Id @GeneratedValue @Column(name = "association_id", unique = true, nullable = false) Long getId() { return id; } public void setId(Long id) { this.id = id; } @ManyToOne @JoinColumn(name = "main_uuid", referencedColumnName = "uuid", nullable = false) public ObjA getMain() { return main; } public void setMain(ObjA main) { this.main = main; } @ManyToOne @JoinColumn(name = "sub_uuid", referencedColumnName = "uuid", nullable = false) public ObjA getSub() { return sub; } public void setSub(ObjA sub) { this.sub = sub; } } 

These mappings have been successfully tested to store values ​​from the uuid column of the obja table in the main_uuid and sub_uuid columns of the association table. This has been tested using org.hibernate.common:hibernate-commons-annotations:4.0.5.Final , org.hibernate.javax.persistence:hibernate-jpa-2.1-api:1.0.0.Final , org.hibernate:hibernate-core:4.3.10.Final and org.hibernate:hibernate-entitymanager:4.3.10.Final for PostgreSQL 9.4.4.