Additional JPA annotations - Foreign key

This annotation is just a simplification, it allows you to combine records that are saved in the database at the same time without using a transaction. The connection is built automatically based on the annotated field. Take, for example, a case where we want to save a master and a detail record in a database that is linked by a foreign key. In this case, the unique key of the master record must be in the detail record. The unique identifier of the master record is determined only after saving (e.g. a sequence-generated value). By default, a save should be made within a transaction - first, we save the master record, then read the primary identifier from it, then save also the detail record. You can see this in the below example:

  Saving a master-detail relationship within a transaction:  
         
SQLTransaction transaction = new SQLTransaction();
try {
    List<DataRecord> savedMasterDataRecords = JpaDaoAPI.save(transaction, Master.class, masterDataRecord);
    detailDataRecord.setValue("masterId", savedMasterDataRecords.get(0).getValue("id");
    JpaDaoAPI.save(transaction, Detail.class, detailDataRecord);
    transaction.commit();
} catch (Exception e) {
    try {
        transaction.rollBack();
    } catch (Exception e2) {
        // Handle rollback error
    }
    // Handle save error
}

By using the ForeignKey annotation (if the save process does not require a transaction), you can replace this process with a simple save statement. Make sure that the list of records passed to the save operation always contains the master record before the detail record, otherwise we will get an error.

  Example of a master entity:  
         
@Entity
public class Master implements Serializable {
    private static final long serialVersionUID = 1;

    @Id
    public Long id;

    /* another column and getter, setter definitions */
}

  Example of a detail record entity:  
         
@Entity
public class Detail implements Serializable {
    private static final long serialVersionUID = 1;

    @Id
    private Long id;

    @ForeignKey(masterEntity=Master.class);

    @ForeignKey(masterEntity=Master.class)
    @Column(name="master_id")
    private Long masterId;

    /* another column and getter, setter definitions */
}

  Implementation of the above example using the foreign key annotation:  
         
JpaDaoAPI.save(Detail.class, masterDataRecord, detailDataRecord);