I hava this class:
@Entity
@Table(name = "USERS")
public class User {
@Id
@Column(name = "USER_ID")
@GeneratedValue
private long userId;
...
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "FRIENDS", joinColumns = @JoinColumn(name = "USER_ID"), inverseJoinColumns = @JoinColumn(name = "FRIEND_ID"))
private Set<User> friends;
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "FRIENDS", joinColumns = @JoinColumn(name = "FRIEND_ID"), inverseJoinColumns = @JoinColumn(name = "USER_ID"))
private Set<User> friendOf;
...
public Set<User> getAllFriends() {
allFriends = new HashSet<User>();
allFriends.addAll(friends);
allFriends.addAll(friendOf);
return allFriends;
}
// getters and seters
If I need all friend of a User I can get them by simply calling getAllFriends(). But I want to add some restriction to the maximum number of returned friends. So I want to select all friends using HQL. I want something like this (my hql is incorrect, just to show the idea):
String hql = "Select u FROM User u inner join u.friendOf fof WHERE fof.userId = :userId inner join u.friends fs WHERE fs.userId = :userId";
Query query = sessionFactory.getCurrentSession().createQuery(hql);
query.setParameter("userId", userId);
List<User> results = query.setMaxResults(maxResults).setFirstResult(firstResult).list();
Is it possible to create such a query?
UPDATE: I have SQL query whiсh fits my requirements. Maybe someone can help me to translate it to HQL?
select * from users where user_id in (
select
(case
when user_id = :userId then friend_id
else user_id
end) as id
from friends
where user_id = :userId or friend_id = :userId);
HQL does not support UNION
clause (there is open issue: https://hibernate.atlassian.net/browse/HHH-1050 ), so this is a little bit harder, but i think you can do something like this:
select u
from User u
where u.userId in (
select fr.userId
from User u1
inner join u1.friends fr
where u1.userId = :userId
)
or u in (
select fr.userId
from User u2
inner join u2.friendOf fr
where u2.userId = :userId
)
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