如何在JPA 2.0中编写带有where子句的MAX查询?
发布于 2021-02-01 12:40:55
我正在使用JPA 2.0。Hibernate 4.1.0.Final和Java6。如何从以下psuedo-SQL编写JPA查询?
select max(e.dateProcessed) from Event e where e.org = myOrg
我的域对象如下所示:
@GenericGenerator(name = "uuid-strategy", strategy = "org.mainco.subco.core.util.subcoUUIDGenerator")
@Entity
@Table(name = "sb__event",
uniqueConstraints = { @UniqueConstraint(columnNames={"EVENT_ID"}) }
)
public class Event
{
@Id
@Column(name = "ID")
@GeneratedValue(generator = "uuid-strategy")
private String id;
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE})
@JoinColumn(name = "ORGANIZATION_ID", nullable = false, updatable = true)
private Organization org;
@Column(name = "DATE_PROCESSED")
@NotNull
private java.util.Date dateProcessed;
我知道涉及CriteriaBuilder.greatest,但是我只是不知道如何编写查询。这将返回所有与组织匹配的事件对象,但据我所知。
final CriteriaBuilder builder = m_entityManager.getCriteriaBuilder();
final CriteriaQuery<Event> criteria = builder.createQuery(Event.class);
final Root<Event> event = criteria.from(Event.class);
criteria.select(event);
criteria.where(builder.equal(Event.get("org"), org));
results.addAll(m_entityManager.createQuery(criteria).getResultList());
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1 个回答
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有两种方法,一种使用JPQL,另一种使用条件查询。
JPQL就是:em.createQuery("select max(e.dateProcessed) from Event e where e.org = :myOrg") .setParameter("myOrg", myOrg) .getSingleResult();
使用条件时,您可能会:
CriteriaBuilder qb = em.getCriteriaBuilder(); CriteriaQuery<Number> cq = qb.createQuery(Number.class); Root<Event> root = cq.from(Event.class); cq.select(qb.max(root.get("dateProcessed"))); cq.where(qb.equal(Event.get("org"), qb.parameter(MyOrgType.class, "myOrg"))); em.createQuery(cq).setParameter("myOrg", myOrg).getSingleResult();