I have 3 POJO classes - Link, LinkDetails and Tag. The relationship between Link and LinkDetails - OneToOne, between LinkDetails and Tag - ManyToMany.
How to use Jpa Criteria, find a list of links with a specified tag name ?
@Entity
public class Link extends AbstractEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column
private String url;
@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
private LinkDetails linkDetails;
}
@Entity
public class LinkDetails extends AbstractEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column
private String description;
@JoinTable(name = "link_details_2_tag", joinColumns = { @JoinColumn(name = "link_details_id")}, inverseJoinColumns = { @JoinColumn(name = "tag_id") })
@ManyToMany(targetEntity = Tag.class, fetch = FetchType.LAZY)
private Set<Tag> tags = new TreeSet<Tag>();
}
@Entity
public class Tag extends AbstractEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column
private String name;
}
@Override
public List<Link> getLinksByTag(String tag){
CriteriaBuilder cBuilder = getEntityManager().getCriteriaBuilder();
CriteriaQuery<Link> criteria = cBuilder.createQuery( Link.class );
Root<Link> linkRoot = criteria.from( Link.class );
Join<Link, LinkDetails> linkDetailsJoin = linkRoot.join(Link_.linkDetails);
Join<LinkDetails, Tag> tagJoin = linkDetailsJoin.join(LinkDetails_.tags);
criteria.select(linkRoot);
criteria.where(cBuilder.equal(tagJoin.get(Tag_.name), tag));
TypedQuery<Link> query = getEntityManager().createQuery(criteria);
return query.getResultList();
}
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