Spring jpa criteriaBuilder search in a list

Question

I have a book class with a list of authors:

@Entity
@Table(name = "book")
public class Book extends Content {

    @ManyToMany(fetch = FetchType.LAZY)
    private List<Author> authors;
...}

Now, this is my BookSpecifications class:

public static Specification<Book> authorIdIs(Long authorId) {
    return new Specification<Book>() {
        @Override
        public Predicate toPredicate(Root<Book> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder cb) {
            return cb.isTrue(root.get("authors").get("id").in(authorId));
        }
    };
}

How can check the given authorId is in the list?

Error:

java.lang.IllegalStateException: Illegal attempt to dereference path source [null.authors] of basic type
    at org.hibernate.jpa.criteria.path.AbstractPathImpl.illegalDereference(AbstractPathImpl.java:98) ~[hibernate-entitymanager-4.3.11.Final.jar:4.3.11.Final]
    at org.hibernate.jpa.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:191) ~[hibernate-entitymanager-4.3.11.Final.jar:4.3.11.Final]
    at com.tarameshgroup.derakht.service.specs.BookSpecifications$3.toPredicate(BookSpecifications.java:40) ~[classes/:na]
    at org.springframework.data.jpa.domain.Specifications$ComposedSpecification.toPredicate(Specifications.java:189) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]

Opheliaophelie

I'm not saying that I'll help, but can you please specify in detail how are you using it? This is a new construct for me, so I do not know, where is the Specification coming from and how to get it executed... It seems to me, the root is not initialized properly see null in [null.authors], but it is not real NPE... – Ingraham

Ok, I found some tutorial - spring.io/blog/2011/04/26/… ... – Ingraham

@Ingraham my problem is in searching in a list , – Opheliaophelie

should be something like builder.equal(root.get("authors").get("id").as(Long.class), authorId) – Henequen

Answer 1

For that you can use Join with predicate:

Refer below code,

public static Specification<Book> authorIdIs(Long authorId) {
    return new Specification<Book>() {
        @Override
        public Predicate toPredicate(Root<Book> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder cb) {
                Join join = root.join("authors");                   
                return cb.equal(join.get("id"),authorId);
        }
    };
}

Rance

@Harsahl What if I need also select authors attributes ? I think join won't do select *.authors automaticlly. – Lesley

@Lesley So you need to get those attributes in join only. – Rance