Spring Data JPA Specification using CriteriaBuilder with a one to many relationship

Question

I have a User entity, a UserToApplication entity, and an Application entity.

A single User can have access to more than one Application. And a single Application can be used by more than one User.

Here is the User entity.

@Entity
@Table(name = "USER", schema = "UDB")
public class User {
    private Long userId;
    private Collection<Application> applications;
    private String firstNm;
    private String lastNm;
    private String email;

    @SequenceGenerator(name = "generator", sequenceName = "UDB.USER_SEQ", initialValue = 1, allocationSize = 1)
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
    @Column(name = "USER_ID", unique = true, nullable = false)
    public Long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    @OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
    public Collection<Application> getApplications() {
        return applications;
    }

    public void setApplications(Collection<Application> applications) {
        this.applications = applications;
    }

    /* Other getters and setters omitted for brevity */
}

Here is the UserToApplication entity.

@Entity
@Table(name = "USER_TO_APPLICATION", schema = "UDB")
public class Application {
    private Long userToApplicationId;
    private User user;
    private Application application;

    @SequenceGenerator(name = "generator", sequenceName = "UDB.USER_TO_APP_SEQ", initialValue = 0, allocationSize = 1)
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
    @Column(name = "USER_TO_APPLICATION_ID", unique = true, nullable = false)
    public Long getUserToApplicationId() {
        return userToApplicationId;
    }

    public void setUserToApplicationId(Long userToApplicationId) {
        this.userToApplicationId = userToApplicationId;
    }

    @ManyToOne
    @JoinColumn(name = "USER_ID", referencedColumnName = "USER_ID", nullable = false)
    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @ManyToOne
    @JoinColumn(name = "APPLICATION_ID", nullable = false)
    public Application getApplication() {
        return application;
    }
}

And here is the Application entity.

@Entity
@Table(name = "APPLICATION", schema = "UDB")
public class Application {
    private Long applicationId;
    private String name;
    private String code;

    /* Getters and setters omitted for brevity */
}

I have the following Specification that I use to search for a User by firstNm, lastNm, and email.

public class UserSpecification {

    public static Specification<User> findByFirstNmLastNmEmail(String firstNm, String lastNm, String email) {
        return new Specification<User>() {
            @Override
            public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
                final Predicate firstNmPredicate = null;
                final Predicate lastNmPredicate = null;
                final Predicate emailPredicate = null;

                if (!StringUtils.isEmpty(firstNm)) {
                    firstNmPredicate = cb.like(cb.lower(root.get(User_.firstNm), firstNm));
                }
                if (!StringUtils.isEmpty(lastNm)) {
                    lastNmPredicate = cb.like(cb.lower(root.get(User_.lastNm), lastNm));
                }
                if (!StringUtils.isEmpty(email)) {
                    emailPredicate = cb.like(cb.lower(root.get(User_.email), email));
                }
                return cb.and(firstNmPredicate, lastNmPredicate, emailPredicate);
            }
        };
    }

}

And here is the User_ metamodel that I have so far.

@StaticMetamodel(User.class)
public class User_ {
    public static volatile SingularAttribute<User, String> firstNm;
    public static volatile SingularAttribute<User, String> lastNm;
    public static volatile SingularAttribute<User, String> email;
}

Now, I would like to also pass in a list of application IDs to the Specification, such that its method signature would be:

public static Specification<User> findByFirstNmLastNmEmailApp(String firstNm, String lastNm, String email, Collection<Long> appIds)

So, my question is, if I add the @OneToMany mapping to the User_ metamodel for the Collection<Application> applications field of my User entity, then how would I reference it in the Specification?

My current Specification would be similar to the following SQL query:

select * from user u
where lower(first_nm) like '%firstNm%'
and lower(last_nm) like '%lastNm%'
and lower(email) like '%email%';

And what I would like to achieve in the new Specification would be something like this:

select * from user u
join user_to_application uta on uta.user_id = u.user_id
where lower(u.first_nm) like '%firstNm%'
and lower(u.last_nm) like '%lastNm%'
and lower(u.email) like '%email%'
and uta.application_id in (appIds);

Is it possible to do this kind of mapping in the metamodel, and how could I achieve this result in my Specification?

Answer 1

I found a solution. To map a one to many attribute, in the metamodel I added the following:

public static volatile CollectionAttribute<User, Application> applications;

I also needed to add a metamodel for the Application entity.

@StaticMetamodel(Application.class)
public class Application_ {
    public static volatile SingularAttribute<Application, Long> applicationId;
}

Then in my Specification, I could access the applications for a user, using the .join() method on the Root<User> instance. Here is the Predicate I formed.

final Predicate appPredicate = root.join(User_.applications).get(Application_.applicationId).in(appIds);

Also, it is worth noting that my Specification as it is written in the question will not work if any of the input values are empty. A null Predicate passed to the .and() method of CriteriaBuilder will cause a NullPointerException. So, I created an ArrayList of type Predicate, then added each Predicate to the list if the corresponding parameter was non-empty. Finally, I convert the ArrayList to an array to pass it to the .and() function of the CriteriaBuilder. Here is the final Specification:

public class UserSpecification {

    public static Specification<User> findByFirstNmLastNmEmailApp(String firstNm, String lastNm, String email, Collection<Long> appIds) {
        return new Specification<User>() {
            @Override
            public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
                final Collection<Predicate> predicates = new ArrayList<>();
                if (!StringUtils.isEmpty(firstNm)) {
                    final Predicate firstNmPredicate = cb.like(cb.lower(root.get(User_.firstNm), firstNm));
                    predicates.add(firstNmPredicate);
                }
                if (!StringUtils.isEmpty(lastNm)) {
                    final Predicate lastNmPredicate = cb.like(cb.lower(root.get(User_.lastNm), lastNm));
                    predicates.add(lastNmPredicate);
                }
                if (!StringUtils.isEmpty(email)) {
                    final Predicate emailPredicate = cb.like(cb.lower(root.get(User_.email), email));
                    predicates.add(emailPredicate);
                }
                if (!appIds.isEmpty()) {
                    final Predicate appPredicate = root.join(User_.applications).get(Application_.applicationId).in(appIds);
                    predicates.add(appPredicate);
                }

                return cb.and(predicates.toArray(new Predicate[predicates.size()]));
            }
        };
    }

}