How to define unidirectional OneToMany relationship in JPA

问题

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?

回答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;

来源：https://stackoverflow.com/questions/12038380/how-to-define-unidirectional-onetomany-relationship-in-jpa

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