Develop Reference

Projections on nested collections

I have three entities Topic, Subject and Category. How can I prefetch id and name columns for each of the entity while retrieving all the categories with subjects and topics? I don't need other fields since it affects the performance.
#Entity
class Topic{
private Long id;
private String name;
...
//other fields
}
#Entity
class Subject{
private Long id;
private String name;
...
//other fields
#OneToMany(fetch=FetchType.LAZY)
private List<Topic> topics;
}
#Entity
class Category{
private Long id;
private String name;
...
//other fields
#OneToMany(fetch=FetchType.LAZY)
private List<Subject> subjects;
}

I would suggest creating a result class on top of the projection itself as it eases the result set handling. The ResultClass needs to have a constructor with relevant query result fields and you have to use the fully qualified name in the query itself.
select new org.mypkg.ResultClass(c.id, c.name, s.id, s.name, t.id, t.name)
from Category c
inner join c.subjects s
inner join s.topics
Then you simply:
List<ResultClass> results = em.createQuery(query).list();

JPA/Hibernate SELECT all parent fields with Child count in Single Query

I am using JPA 2.0, with Hibernate 1.0.1.Final.
I want all Parent table fields with no of children in single query.
In Other word, I want to translate from SQL into CriteriaAPI of JPA/Hibernate.
select kgroup.*, count(userGroup.uid)
from kernelGroup kgroup
left join kernelUserGroup userGroup on (kgroup.groupId = userGroup.groupId)
group by kgroup.groupId
I have following JPA Entities.
#Entity
#Table(name="kernel_group")
public class KernelGroup implements Serializable {
#Id
private int groupId;
private boolean autoGroup;
private String groupName;
#OneToMany
private Set<KernelUserGroup> kernelUserGroups;
private long jpaVersion;
}
#Entity
#Table(name="kernel_usergroup")
public class KernelUserGroup implements Serializable {
#EmbeddedId
private KernelUserGroupPK id;
private long jpaVersion;
#ManyToOne
private KernelGroup kernelGroup;
#ManyToOne
private KernelUser kernelUser;
}
#Embeddable
public class KernelUserGroupPK implements Serializable {
private String uid;
private int groupId;
}
My Current Criteria Query is like this :
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<KernelGroupDto> cQuery = cb.createQuery(KernelGroupDto.class);
Root<KernelGroup> root = cQuery.from(KernelGroup.class);
Join<KernelGroup, KernelUserGroup> userGroupsJoin = root.join(KernelGroup_.kernelUserGroups, JoinType.LEFT);
cQuery.select(cb.construct(KernelGroupDto.class, root, cb.count(userGroupsJoin.get(KernelUserGroup_.id).get(KernelUserGroupPK_.uid))));
cQuery.groupBy(root.get(KernelGroup_.groupId));
em.createQuery(cQuery).getResultList();
Now the Problem is, It fires multiple Queries to the database.
1) One query to retrieve groupId and no of count of users
2) N Queries to retrieve group info for each group.
I want only one Query to retrieve GroupInfo and no of count of the users as shown in Above SQL Query.
Please give me good suggestion.

Implement Using the bellow Code.
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<KernelGroupDto> cQuery = cb.createQuery(KernelGroupDto.class);
Root<KernelGroup> root = cQuery.from(KernelGroup.class);
Join<KernelGroup, KernelUserGroup> userGroupsJoin =
root.join(KernelGroup_.kernelUserGroups, JoinType.LEFT);
cQuery.select(cb.construct(KernelGroupDto.class, root.
<Long>get("id"),cb.count(userGroupsJoin)));
cQuery .groupBy( root.<Long>get("id") );
cQuery.groupBy(root.get(KernelGroup_.groupId));
em.createQuery(cQuery).getResultList();
This code will work. for child count.
you must have the constructor of the class KernelGroupDto(Long id, Long childCount)

Hibernate Criteria on Referenced table

I have a function that merges two tables, each of these tables has a column that I want to filter.
#Entity
public class Contacts {
#Id
private int id;
#ManyToOne //reference user_id = id
private User user;
#ManyToOne //reference people_id = id
private People people;
//getters and setters
}
#Entity
public class User {
private int id;
private int name;
private Enterprise enterprise;
//getters and setters
}
#Entity
public class People {
private int id;
private int name;
//..others fields
private Enterprise enterprise;
//getters and setters
}
I need to list all "Contacts" where my enterprise id = 1. On a simple select (SQLServer), it will be:
SELECT c.* FROM CONTACTS c
INNER JOIN User u ON u.id = c.user_id
INNER JOIN People p on p.id = p.people_id
WHERE u.empresa_id = 1
I can't figure out how to do it with Criteria API, I already tried the follow code, but I keep receiving an error.
//code..public List<Obj> list(int id) {
Criteria crit = session.createCriteria(Contacts.class);
crit.add(Restrictions.eq(user.enterprise.id, id)); //it doesn't work!
crit.list();
}
org.hibernate.QueryException: could not resolve property: user.enterprise.id of: sys.com.model.Contacts

here i am writing code for sample using criteria.
public List<Student_document> getUserById(int id) {
Criteria criteria = sessionFactory.getCurrentSession().createCriteria(
Student_document.class);
criteria.add(Restrictions.eq("user_document.user_Id", id));
return criteria.list();
}

Hibernate criteria on embedded id member member value

I would like to find an entity using a critera with restriction on the value of an attribute of a second entity wich is a member of the embedded id of my first entity.
First entity :
#Entity
public class Car {
#EmbeddedId
private Id id = new Id();
private String color;
#Embeddable
public static class Id implements Serializable {
private static final long serialVersionUID = -8141132005371636607L;
#ManyToOne
private Owner owner;
private String model;
// getters and setters...
// equals and hashcode methods
}
// getters and setters...
}
Second entity :
#Entity
public class Owner {
#Id
#GeneratedValue (strategy = GenerationType.AUTO)
private Long id;
private String firstname;
private String lastname;
#OneToMany (mappedBy = "id.owner")
private List<Car> cars;
// getters and setters...
}
In this example, I would like to obtain the car with the color 'black', model 'batmobile' and the owner's firstname 'Bruce' (oops... spoiler ;) )
I tried to do something like that but it won't work :
List<Car> cars = session.createCriteria(Car.class)
.add(Restrictions.eq("color", "black"))
.add(Restrictions.eq("id.model", "batmobile"))
.createAlias("id.owner", "o")
.add(Restrictions.eq("o.firstname", "Bruce"))
.list();
Result :
Hibernate: select this_.model as model1_0_0_, this_.owner_id as owner_id3_0_0_, this_.color as color2_0_0_ from Car this_ where this_.color=? and this_.model=? and o1_.firstname=?
ERROR: Unknown column 'o1_.firstname' in 'where clause'
What is the right way to obtain what I want ?
update
I tried in hql :
String hql = "FROM Car as car where car.color = :color and car.id.model = :model and car.id.owner.firstname = :firstname";
Query query = em.createQuery(hql);
query.setParameter("color", "black");
query.setParameter("model", "batmobile");
query.setParameter("firstname", "Bruce");
List<Car> cars = query.getResultList();
It works but is there a way to do this with criteria ?

You forgot to add the #Column annotation on top of the firstname and lastname fields (and the color field in Car). In hibernate if a field is not annotated, it doesn't recognize it as a database field. This page should give you a good idea about how to set up your model objects.
NOTE: You can have the column annotation over the getters and be fine, but you didn't show the getters. Either place is fine.
Look at what HQL is spitting back out, specifically the statement (formated for easier reading):
select
this_.model as model1_0_0_,
this_.owner_id as owner_id3_0_0_,
this_.color as color2_0_0_
from Car this_
where
this_.color=?
and this_.model=?
and o1_.firstname=?
It looks like hibernate is translating the field "id.owner" to "o" as your alias told it to to, but for some reason it's not writing down that "id.owner=o" as intended. You may want to do some research into why it may be doing that.

As per https://hibernate.atlassian.net/browse/HHH-4591 there is a workaround.
You have to copy the needed relation-property of the #EmbeddedId (owner in this case) to the main entity (Car in this case) with insertable = false, updatable = false as follows
#Entity
public class Car {
#EmbeddedId
private Id id = new Id();
private String color;
#ManyToOne
#JoinColumn(name = "column_name", insertable = false, updatable = false)
private Owner owner;
#Embeddable
public static class Id implements Serializable {
private static final long serialVersionUID = -8141132005371636607L;
#ManyToOne
private Owner owner;
private String model;
// getters and setters...
// equals and hashcode methods
}
// getters and setters...
}
Then just create directly the alias instead of using the composite id property
List<Car> cars = session.createCriteria(Car.class)
.add(Restrictions.eq("color", "black"))
.add(Restrictions.eq("id.model", "batmobile"))
.createAlias("owner", "o")
.add(Restrictions.eq("o.firstname", "Bruce"))
.list();

Using MEMBER OF with a collection of entities identified by a composite key

I am trying to return a set of objects that are not part of a collection like this:
TypedQuery<Extra> q = em
.createQuery(
"SELECT e FROM Extra e, Arrangement a WHERE "
+ "a.id = :arrid AND e NOT MEMBER OF a.extras",
Extra.class);
q.setParameter("arrid", a.getId());
return q.getResultList();
But I get a bad SQL out of this:
Caused by: org.h2.jdbc.JdbcSQLException: Subquery is not a single column query; SQL statement:
select extra0_.code as code427_, extra0_.edition_number as edition5_427_,
extra0_.totalCost as totalCost427_, extra0_.unitCost as unitCost427_,
extra0_.units as units427_ from extra_arrangements extra0_
cross join arrangements arrangemen1_
where arrangemen1_.id=? and
((extra0_.code, extra0_.edition_number) not in
(select extra3_.code, extra3_.edition_number
from arrangements_extra_arrangements extras2_, extra_arrangements extra3_
where arrangemen1_.id=extras2_.arrangements_id and
extras2_.extras_code=extra3_.code and
extras2_.extras_edition_number=extra3_.edition_number)) [90052-161]
The thing is that this other query works as expected:
TypedQuery<Exhibitor> q = em.createQuery(
"SELECT e FROM Exhibitor e, Edition ed WHERE ed.number = :ednum AND "
+ "e NOT MEMBER OF ed.exhibitors",
Exhibitor.class);
q.setParameter("ednum", e.getNumber());
return q.getResultList();
The only difference being that Exhibitor has a single column id, whereas Extra has a composite key:
#Entity
#Table(name = "exhibitors")
public class Exhibitor implements Serializable, Comparable<Exhibitor> {
#Id
private int id;
#Column(length = 100)
private String code;
#ManyToMany
private List<Edition> edition;
...
}
Extra:
#Entity
#Table(name="extra_arrangements")
public class Extra implements Serializable {
#EmbeddedId
private ExtraCode id;
private double unitCost;
private double units;
...
}
#Embeddable
public class ExtraCode implements Serializable {
private String code;
#ManyToOne
private Edition edition;
//Getters and setters omitted
}
Any idea what I might be doing wrong and how to fix it?

I think it's same problem as this one.
H2 does not currently support that style of IN query.
Problematic place in sql-query:
AND (
(
extra0_.code,
extra0_.edition_number
) NOT IN
(SELECT ...)
)