Atul Chaudhary :
I have got three classes as mentioned below. I am trying to create a specification to filter data where there is a match in the linked table.
public class Album {
private Long id;
private List<AlbumTag> albumTags;
}
public class Tag {
private Long id;
private String category;
}
public class AlbumTag{
private Long id;
private Album album;
private Tag tag;
}
In the schema given above what I am trying to find is a list of all albums from Album table with the link in AlbumTag. The SQL that I want to achieve, doesn't have to be same, is below
select *
from Album A
where (A.Id in (select [AT].AlbumId
from AlbumTag [AT]))
What I have tried so far which is not working, of course, is below
public class AlbumWithTagSpecification implements Specification<Album> {
@Override
public Predicate toPredicate(Root<Album> root, CriteriaQuery<?> cq, CriteriaBuilder cb) {
final Subquery<Long> personQuery = cq.subquery(Long.class);
final Root<Album> album = personQuery.from(Album.class);
final Join<Album, AlbumTag> albumTags = album.join("albumTags");
personQuery.select((albumTags.get("album")).get("id"));
personQuery.where(cb.equal(album.get("id"), (albumTags.get("album")).get("id")));
return cb.in(root.get("id")).value(personQuery);
}
}
Praveen D :
Using spring boot and spring data JPA, you can prefer entity relationship to fetch the data.
1.Annotate the domain class with the entity relationship which given below:
@Entity
@Table(name="Album")
public class Album {
@Id
@Column(name="id")
private Long id;
@OneToMany(targetEntity = AlbumTag.class, mappedBy = "album")
private List<AlbumTag> albumTags;
//getter and setter
}
@Entity
@Table(name="Tag")
public class Tag {
@Id
@Column(name="id")
private Long id;
@Column(name="category")
private String category;
//getter and setter
}
@Entity
@Table(name="AlbumTag")
public class AlbumTag{
@Id
@Column(name="id")
private Long id;
@ManyToOne(optional = false, targetEntity = Album.class)
@JoinColumn(name = "id", referencedColumnName="id", insertable = false, updatable = false)
private Album album;
@ManyToOne(optional = false, targetEntity = Tag.class)
@JoinColumn(name = "id", referencedColumnName="id", insertable = false, updatable = false)
private Tag tag;
//getter and setter
}
2.use the spring data to fetch the details using the below:
Album album = ablumRepository.findOne(1); // get the complete details about individual album.
List<AlbumTag> albumTags = ablum.getAlbumTags(); // get the all related albumTags details for particular album.
I hope this will help you to solve it.
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