JPA - @OneToMany as a Map

Question

This seems like a common enough case, but as JPA newbie, I am having trouble figuring this out. I'm using EclipseLink and PostgreSQL, but this should relate to just the JPA spec.

I have one table PRIMARY that has an ID and then a bunch of other columns. There is another table SECONDARY that has a foreign key into the PRIMARY table also called ID. This SECONDARY table has a composite key of that ID and a varchar representing a locale.

So, in the Primary entity I want to have a field of type Map<String, Secondary> where the key is the locale string from the SECONDARY table and the entry is the Secondary entity. My Secondary class looks like this:

@Entity
public class Secondary
{
     @Id
     private Long id;
     @Id
     private String locale;
     private String str1;
     private String str2;
     .....
}

I'm thinking I want to use the @MapKeyJoinColumn annotation, but I can't seem to get the other annotations to work. I tried this:

@OneToMany
@JoinColumn(name="ID")
@MapKeyJoinColumn(name="LOCALE")
private Map<String, Secondary> secondaryByLocale;

This resulted in it trying to select a column named secondaryByLocale_key which doesn't exist.

I then tried this:

@OneToMany
@JoinTable(name="SECONDARY", 
        joinColumns={@JoinColumn(name="ID")},
        inverseJoinColumns=@JoinColumn(name="ID"))
@MapKeyJoinColumn(name="LOCALE")
private Map<String, Secondary> secondaryByLocale;

This results in the following error:

Exception Description: The @JoinColumns on the annotated element [field secondaryByLocale] from the entity class [class com.foo.Primary] is incomplete. When the source entity class uses a composite primary key, a @JoinColumn must be specified for each join column using the @JoinColumns. Both the name and the referencedColumnName elements must be specified in each such @JoinColumn.

I tried adding the referencedColumnName to the annotation (I wasn't sure what it even should be), but I got the same error.

As suggested, I tried using @MapKey as follows:

@OneToMany
@JoinColumn(name="ID")
@MapKey(name="LOCALE")
private Map<String, Secondary> secondaryByLocale;

This results in the following error:

Exception Description: The map key [LOCALE] on the entity class [class com.foo.Secondary] could not be found for the mapping [org.eclipse.persistence.mappings.UnidirectionalOneToManyMapping[secondaryByLocale]].

Maybe I'm going about this all wrong, and there's a better way to annotate the Map field. Any help would be much appreciated.

Cornaceous

Answer 1

Try using @MapKey(name = "locale") instead.

@MapKeyJoinColumn is used when your map key is an entity, but here you're just using the locale String.

Basifixed

If that doesn't work, can you post the code for your Secondary class? – Basifixed

I've updated the question with the Secondary code and the results from trying @MapKey – Cornaceous

I've updated my answer - your entity attribute is called "locale" not "LOCALE"... – Basifixed

Also, are you sure it's valid to have two @Id fields on your Secondary entity? – Basifixed

Interesting, I haven't had any problems with case sensitivity before, but that definitely fixes it. Also, the two @Id annotations seem to work just fine. Thanks so much for your help! – Cornaceous

Great :-) With case sensitivity, you'll have mixed results when you're referring to table column names but here you're referring to a class property (to be used as a Map key) so definitely case sensitive. – Basifixed

Answer 2

In my case, it is worked with @OneToMany(cascade=CascadeType.PERSIST) @MapKeyColumn(name="COLUMN_NAME")

or

You can directly try with only @OneToMany(cascade=CascadeType.PERSIST)

Philipp