Re: how to specify index / unique constraint on multiple columns of a container table?

[Andy Schlaikjer]

This doesn't quite work.. OpenJPA 1.2.0 complains about Alias (an 
Embeddable) not having an identity type:

org.apache.openjpa.persistence.ArgumentException: Cannot manipulate 
identity of type "edu.cmu.hazen.domain.Alias": it's identity type is 
unknown.


Andy Schlaikjer wrote:
I think may I've figured it out. It seems I can use a @JoinTable along 
with @PersistentCollection to achieve something like this:

@Embeddable
public class Alias {
  private String value;
  private int frequency;
}

@Entity
public class Person {
  @Id
  private long id;

  @PersistentCollection(elementEmbedded = true)
  @ElementDependent
  @JoinTable(
    name = "PersonAlias",
    joinColumns = @JoinColumn(name = "person_id"),
    uniqueConstraints = @UniqueConstraint(
      columnNames = { "person_id", "value" }
    )
  )
  @OrderBy(value = "frequency desc, value asc")
  private SortedSet<Alias> aliases;
}

CREATE TABLE Person (id BIGINT NOT NULL, PRIMARY KEY (id))
CREATE TABLE PersonAlias (person_id BIGINT NOT NULL, value VARCHAR(255) 
NOT NULL, frequency INTEGER, UNIQUE UNQ_person_idvalue (person_id, value))

-Andy