Enterprise Java Development@TOPIC@

Chapter 58. Relationship Capabilities

58.1. Fetching
58.1.1. fetch=LAZY
58.1.2. fetch=EAGER
58.2. Cascades
58.3. Orphan Removal
58.4. Summary

58.1. Fetching

Figure 58.1. fetch=LAZY Example Declaration

@OneToMany(mappedBy="borrower", //this relationship is owned by Checkout

        fetch=FetchType.LAZY)

private Collection<Checkout> checkouts = new ArrayList<Checkout>();

  • @XxxToXxx Relationship annotated with fetch=LAZY property

Figure 58.2. fetch=LAZY Example Use

Borrower borrower2 = em.find(Borrower.class, borrower.getId());

log.info("found borrower: " + borrower.getName());

assertEquals(6, borrower2.getCheckouts().size());

  • Parent accessed, debug printed, and then child collection accessed

Figure 58.3. fetch=LAZY SQL Output

Hibernate: 
    select
        applicant0_.id as id1_12_2_,
        applicant0_.APP_BORROWER as APP2_12_2_,
        applicant0_.APP_PERSON as APP3_12_2_,
        borrower1_.BORROWER_ID as BORROWER1_15_0_,
        borrower1_.endDate as endDate2_15_0_,
        borrower1_.startDate as startDat3_15_0_,
        person2_.PERSON_ID as PERSON1_24_1_,
...
        person2_.PERSON_PHOTO as PERSON5_24_1_ 
    from ORMREL_APPLICANT applicant0_ 
    left outer join ORMREL_BORROWER borrower1_ 
            on applicant0_.APP_BORROWER=borrower1_.BORROWER_ID 
    inner join ORMREL_PERSON person2_ 
            on applicant0_.APP_PERSON=person2_.PERSON_ID 
    where applicant0_.APP_BORROWER=?

-found borrower: john smith

Hibernate: 
    select
        checkouts0_.CHECKOUT_BID as CHECKOUT4_15_1_,
        checkouts0_.CHECKOUT_ID as CHECKOUT1_16_1_,
        checkouts0_.CHECKOUT_ID as CHECKOUT1_16_0_,
        checkouts0_.CHECKOUT_BID as CHECKOUT4_16_0_,
        checkouts0_.outDate as outDate2_16_0_,
        checkouts0_.returnDate as returnDa3_16_0_ 
    from ORMREL_CHECKOUT checkouts0_ 
    where checkouts0_.CHECKOUT_BID=?

  • Debug for parent printed before child rows retrieved

  • Child rows retrieved when parent collection accessed

Figure 58.4. fetch=EAGER Example Declaration

@OneToMany(mappedBy="borrower", //this relationship is owned by Checkout

        fetch=FetchType.EAGER)

private Collection<Checkout> checkouts = new ArrayList<Checkout>();

Figure 58.5. fetch=EAGER Example Use



Borrower borrower3 = em.find(Borrower.class, borrowerId);

log.info("found borrower: " + borrower.getName());

assertEquals(0,borrower3.getCheckouts().size());        

  • Same as fetch=LAZY case

Figure 58.6. fetch=EAGER SQL Output

Hibernate: 
    select
        applicant0_.id as id1_12_3_,
        applicant0_.APP_BORROWER as APP2_12_3_,
        applicant0_.APP_PERSON as APP3_12_3_,
        borrower1_.BORROWER_ID as BORROWER1_15_0_,
        borrower1_.endDate as endDate2_15_0_,
        borrower1_.startDate as startDat3_15_0_,
        checkouts2_.CHECKOUT_BID as CHECKOUT4_15_5_,
        checkouts2_.CHECKOUT_ID as CHECKOUT1_16_5_,
        checkouts2_.CHECKOUT_ID as CHECKOUT1_16_1_,
        checkouts2_.CHECKOUT_BID as CHECKOUT4_16_1_,
        checkouts2_.outDate as outDate2_16_1_,
        checkouts2_.returnDate as returnDa3_16_1_,
        person3_.PERSON_ID as PERSON1_24_2_,
...
        person3_.PERSON_PHOTO as PERSON5_24_2_ 
    from ORMREL_APPLICANT applicant0_ 
    left outer join ORMREL_BORROWER borrower1_ 
            on applicant0_.APP_BORROWER=borrower1_.BORROWER_ID 
    left outer join ORMREL_CHECKOUT checkouts2_ 
            on borrower1_.BORROWER_ID=checkouts2_.CHECKOUT_BID 
    inner join ORMREL_PERSON person3_ 
            on applicant0_.APP_PERSON=person3_.PERSON_ID 
    where applicant0_.APP_BORROWER=?

-found borrower: john smith

  • Child objects fetched with parent

  • Access to child collection occurs after all children fetched

58.2. Cascades

Figure 58.7. 

@Entity

@Table(name="RELATIONEX_LICAPP")

public class LicenseApplication {

    @Id @GeneratedValue

    private int id;

    @Temporal(TemporalType.TIMESTAMP)

    private Date updated;

    

    @OneToOne(optional=false, fetch=FetchType.EAGER, 

            cascade={

                CascadeType.PERSIST,

                CascadeType.DETACH,

                CascadeType.REMOVE,

                CascadeType.REFRESH,

                CascadeType.MERGE

            })

    private License license;

PERSIST

Related entities persisted when this entity is passed to em.persist()

DETACH

Related entities detached from persistence unit when this entity passed to em.detach()

REMOVE

Related entities deleted from database when this entity passed to em.remove()

REFRESH

Related entities refreshed with state of database when this entity passed to em.refresh()

MERGE

Related entities update state of database when this entity is passed to em.merge()

58.3. Orphan Removal

Figure 58.8. OrphanRemoval Example Declaration



@Entity

@Table(name="RELATIONEX_ATTENDEE")

public class Attendee {

    @Id @GeneratedValue

    private int id;

    

    //orphanRemoval will take care of dereference and DELETE from dependent Attendee 

    @OneToOne(cascade=CascadeType.PERSIST, orphanRemoval=true)

    private Residence residence;

Figure 58.9. Triggering OrphanRemoval

attendee.setResidence(null);

em.flush();

Figure 58.10. OrphanRemoval Database Interaction

Hibernate: 
    update RELATIONEX_ATTENDEE 
    set name=?, residence_id=? 
    where id=?
Hibernate: 
    delete from RELATIONEX_RESIDENCE 
    where id=?

  1. Attendee.residence_id set to null

  2. Orphaned residence deleted

58.4. Summary