JPA and non-primitive ElementCollection

Question

I've got two tables in my database that look like this, with a foreign key from job_label.job_id to equivalent column in job_record . Additionally, the triple of job_id , label_key , and label in job_record has a unique constraint.

mysql> select * from job_record;
+--------+---------+
| job_id | state   |
+--------+---------+
|      1 | success |
|      2 | running |
|      3 | errored |
|      4 | success |
+--------+---------+

mysql> select * from job_label
+--------+-----------+--------+
| job_id | label_key | label  |
+--------+-----------+--------+
|      1 | name      | job 1  |
|      1 | type      | normal |
+--------+-----------+--------+

On the Java class side I have this class:

@Entity
@Table(name = "job_record")
public class JobRecord {

    @Id
    @Column(name = "job_id")
    private String jobId;

    @Enumerated(EnumType.STRING)
    @Column(name = "state")
    private JobState state;
}

I've tried to define a class for job_label that looks something like this:

public class JobLabelRecord {
    @Enumerated(EnumType.STRING)
    @Column(name = "label_key")
    private JobLabelKey key;

    @Column(name = "label")
    private String label;
}

And then I want a field in JobRecord that provides me all labels for that Job as a List<JobLabelRecord> . However, nothing I've tried works.

I've tried declaring JobLabelRecord as Embeddable with the equivalent field in JobRecord as Embedded . I've tried using ManyToOne and OneToMany mappings, but that fails because there's no Id columns in JobLabelRecord (and nothing I do with those works correctly).

Am I supposed to be using an ElementCollection here instead? I've tried that as well, but without success.

Any ideas here? Thanks!

Answer 1

You can find a simple example for this by searching for "jpa elementcollection separate table", such as JPA Tutorial - JPA ElementCollection CollectionTable Override Example . Applying this example to your problem gives the following:

@Entity
@Table(name = "job_record")
public class JobRecord {

    @Id
    @Column(name = "job_id")
    private Integer jobId;

    @Enumerated(EnumType.STRING)
    @Column(name = "state")
    private JobState state;

    @ElementCollection
    @CollectionTable(name="job_label",
           joinColumns=@JoinColumn(name="job_id")) 
    private List<JobLabelRecord> labels;
...

@Embeddable
public class JobLabelRecord {
    @Enumerated(EnumType.STRING)
    @Column(name = "label_key")
    private JobLabelKey key;

    @Column(name = "label")
    private String label;
...

Note also the JobRecord id should probably be an Integer .