CODEWITHSUNDEEP
javasqlhibernatejpajpa-2.0
John
John

Reputation: 593

How to build a JPA 2.0 query

I have two entities: Event and Comment. 

@Entity
@Table(name = "events")
public class Event extends BaseEntity {
    @Id
    @Column(name = "event_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Long eventId;

    @Column(name = "title", length = 200)
    protected String title;

    @OneToMany(mappedBy = "event", cascade = CascadeType.REMOVE)
    @LazyCollection(LazyCollectionOption.FALSE)
    protected List<Comment> comments;
}

@Entity
@Table(name = "comments")
public class Comment extends BaseEntity {
    @Id
    @Column(name = "comment_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Long commentId;

    @ManyToOne(optional = false)
    @JoinColumn(name = "event_id", referencedColumnName="event_id", nullable = false)
    protected Event event;

    @Column(name = "update_time", nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    protected Date updatedTimestamp;
}

So each event has a list of comments and each comment has an update time.

I want to use Criteria API to construct a query such that choose all events that has at least one new comments. (New comment means its update time is later than a given date time)

Thanks for anyone helping me.

Sorry the question I asked above is not complete: what I want is use Criteria API to construct a query such that choose all events that has at least one new comments and eventId is equal to some specific eventId.

I have tried: (Given Date lastCheckedTime and Long eventId)

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Event> cq = cb.createQuery(Event.class);
Root<Comment> c = cq.from(Comment.class);
Predicate lastCheckedTimeCondition = cb.greaterThanOrEqualTo(
     c.get(Comment_.updatedTimestamp), lastCheckedTime);
cq.where(lastCheckedTimeCondition);
cq.select(c.get(Comment_.event));
TypedQuery<Event> query = em.createQuery(cq);
result = query.getResultList();

the above code can choose events that have new comments but now I don't know how to add the conditon about the eventId.

Upvotes: 0

Views: 559

Answers (2)

JB Nizet
JB Nizet

Reputation: 692131

Create a join on the event, and apply the restriction on the ID of the event:

Join<Comment, Event> event = c.join(Comment_.event);
Predicate eventIdPredicate = cb.eq(event.get(Event_.eventId), theEventId);

And then use CriteriaBuilder's and method to combine the two predicates into one as shown by Lukas's answer.

Upvotes: 1

Lukas Eder
Lukas Eder

Reputation: 221220

CriteriaBuilder has an and(Predicate...) method. You would then connect your two predicates:

cq.where(cb.and(lastCheckedTimeCondition, someEventIdCondition));

Upvotes: 1

Related Questions