How to define unidirectional OneToMany relationship in JPA

Question

I have a following problem with entity mapping in JPA. I have two entities, first one is Lookup and the second is Text which represents translations for entities. Now I need to bound Lookup to the Text but I don't want Text to have reference to Lookup. To make this more complicated, Text does not use its primary key in this relationship but a metacode defined in a TXTHEAD_CODE column.

Lookup.java

@Entity @Table(name = "DATREG") public class Lookup implements PersistableEntity {      @Id     @Column(name = "DATREG_META_CODE")     private String metaCode;      @OneToMany     @JoinTable(name="TXT",              joinColumns=@JoinColumn(name="DATREG_META_CODE", referencedColumnName="TXTHEAD_CODE"),             inverseJoinColumns=@JoinColumn(name="DATREG_META_CODE"))     private List<Text> text; 

Text.java

@Entity @Table(name = "TXT") public class Text {      @Id     @Column(name = "TXT_ID")     private Long id;      @Column(name = "TXTHEAD_CODE")     private String code; 

So I have tried this (and few other variations) but with no result. I also can't create join table in the DB and I don't want bound Lookup to my Text class. So can anyone please tell me if there is some other way?

Answer 1

My bible for JPA work is the Java Persistence wikibook. It has a section on unidirectional OneToMany which explains how to do this with a @JoinColumn annotation. In your case, i think you would want:

@OneToMany @JoinColumn(name="TXTHEAD_CODE") private Set<Text> text; 

I've used a Set rather than a List, because the data itself is not ordered.

The above is using a defaulted referencedColumnName, unlike the example in the wikibook. If that doesn't work, try an explicit one:

@OneToMany @JoinColumn(name="TXTHEAD_CODE", referencedColumnName="DATREG_META_CODE") private Set<Text> text;