特定
@Entity
public class Document {
@Id
@Column(name = "DOCUMENT_ID")
private Long id;
@ElementCollection
@CollectionTable(
name="TAG",
joinColumns=@JoinColumn(name="DOCUMENT_ID")
)
@Column(name="TAG")
private Set<String> tags;
}
找到标有标签的特定集合中的所有文件。 从本质上讲,一个的EclipseLink等价的:
SELECT d FROM Document d WHERE :tag1 MEMBER OF d.tags
INTERSECT
SELECT d FROM Document d WHERE :tag2 MEMBER OF d.tags
...
SELECT d FROM Document d WHERE :tagn MEMBER OF d.tags
但使用JPA CritieraQuery。
使用聚合查询与having子句来选择匹配所有需要的标签行:
CriteriaBuilder cb = entityManager().getCriteriaBuilder();
CriteriaQuery<Long> q = cb.createQuery(Long.class);
Root<Document> from = q.from(Document.class);
List<Predicate> predicates = new ArrayList<Predicate>();
Expression<Long> id = from.get("id");
Expression<Collection<String>> documentTags = from.get("tags");
for (String tag : searchedTags) {
Expression<String> param = cb.literal(tag);
Predicate predicate = cb.isMember(param, documentTags);
predicates.add(predicate);
}
q.multiselect(id).where(
cb.or(predicates.toArray(new Predicate[0])));
q.distinct(true);
q.groupBy(id);
q.having(cb.equal(cb.count(id), searchedTags.size()));
TypedQuery<Long> query = entityManager().createQuery(q);