How is it possible to access pre-filtered dependent entities from Associations retrieved via JPA/Hibernate criteria query with restrictions? - jpa

Question

I have a provider:user=1:N association modeled with entities, Hibernate/JPA.
Then I want to query a provider/user pair via restrictions on attributes of the dependent entity, like certain values for the attributes of the user, let’s say its id, date of birth, etc.
The logged sql has a proper join and all the attributes of the two entities in the select. I tried it manually, it returns the expected single row.
Thus, on entity level, I expect a single provider entity to be returned with the user list containing the queried user.
Indeed, the corresponding provider entity is returned, but when I then want to access the user via the provider’s user list, it hits the DB a second time and reads all users of the provider totally neglecting my restrictions of the query.
The observed behavior is the same for queries formulated with HQL, Hibernate Criteria (also with #Filter), JPA CriteriaBuilder.
What am I missing here?
Do those restrictions only affect the selection of the root entities (which is provider in my case)?
The problem is sketched on
https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html
Under 5.4 Associations it says:
The kittens collections held by the Cat instances returned by the previous two queries are not pre-filtered by the criteria. If you want to retrieve just the kittens that match the criteria, you must use a ResultTransformer.
Is this thus the intended behavior for this kind of API?
Or is there a convenient possibility to access just the restricted sub set of the dependent entities?
Regards,
Wolfgang

Answer 1

Here comes some source code to precise my verbal description above.
Provider and User table.
drop table EX_USER;
drop table EX_PROVIDER;
create table EX_PROVIDER
( id number(*,0) not null
,name varchar2(255) not null
,primary key (id)
);
insert into EX_PROVIDER (id,name) values (0 ,'Provider_A');
insert into EX_PROVIDER (id,name) values (1 ,'Provider_B');
commit;
create table EX_USER
( id number(*,0) not null
, ex_provider_id number(*,0) not null
,name varchar2(255)
,location varchar2(255)
,primary key (id)
,constraint ex_user_provider_fk foreign key(ex_provider_id) references EX_PROVIDER(id)
);
insert into EX_USER (id,ex_provider_id,name,location) values (0,0,'User_1','Munich');
insert into EX_USER (id,ex_provider_id,name,location) values (1,0,'User_2','Berlin');
insert into EX_USER (id,ex_provider_id,name,location) values (2,1,'User_3','Munich');
commit;
Entities generated with Eclipse "JPA Tools".
#Entity
#Table(name="EX_PROVIDER")
#NamedQuery(name="ExProvider.findAll", query="SELECT e FROM ExProvider e")
public class ExProvider implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#SequenceGenerator(name="EX_PROVIDER_ID_GENERATOR", sequenceName="KONST_SD_SEQ")
#GeneratedValue(strategy=GenerationType.SEQUENCE, generator="EX_PROVIDER_ID_GENERATOR")
private long id;
private String name;
//bi-directional many-to-one association to ExUser
#OneToMany(mappedBy="exProvider",fetch=FetchType.LAZY)
private Set<ExUser> exUsers=new HashSet<ExUser>();
public ExProvider() {
}
public long getId() {
return this.id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public Set<ExUser> getExUsers() {
return this.exUsers;
}
public void setExUsers(Set<ExUser> exUsers) {
this.exUsers = exUsers;
}
public ExUser addExUser(ExUser exUser) {
getExUsers().add(exUser);
exUser.setExProvider(this);
return exUser;
}
public ExUser removeExUser(ExUser exUser) {
getExUsers().remove(exUser);
exUser.setExProvider(null);
return exUser;
}
}
#Entity
#Table(name="EX_USER")
#NamedQuery(name="ExUser.findAll", query="SELECT e FROM ExUser e")
public class ExUser implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#SequenceGenerator(name="EX_USER_ID_GENERATOR", sequenceName="KONST_SD_SEQ")
#GeneratedValue(strategy=GenerationType.SEQUENCE, generator="EX_USER_ID_GENERATOR")
private long id;
private String location;
private String name;
//bi-directional many-to-one association to ExProvider
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="EX_PROVIDER_ID")
private ExProvider exProvider;
public ExUser() {
}
public long getId() {
return this.id;
}
public void setId(long id) {
this.id = id;
}
public String getLocation() {
return this.location;
}
public void setLocation(String location) {
this.location = location;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public ExProvider getExProvider() {
return this.exProvider;
}
public void setExProvider(ExProvider exProvider) {
this.exProvider = exProvider;
}
}
My intention with the below code was to retrieve Provider 0 (Provider_A) containing User 1 (Berlin) in its user list.
#SuppressWarnings("unchecked")
private void demo() {
EntityManager em = null;
try {
em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
try {
tx.begin();
Session session = (Session) em.getDelegate();
Criteria crit = session.createCriteria(ExProvider.class, "provider")
.createCriteria("exUsers", "user")
.add(Restrictions.eq("user.location","Berlin"))
;
List<ExProvider> providerList=(List<ExProvider>)crit.list();
logExProviderList(providerList);
tx.commit();
} finally {
if (tx!=null && tx.isActive()) tx.rollback();
}
} finally {
if (em!=null) em.close();
}
}
private void logExProviderList(List<ExProvider> providerList) {
for (ExProvider provider: providerList) {
logger.info("Criteria: provider=["+provider.getId()+"]");
for (ExUser user : provider.getExUsers()) {
logger.info("Criteria: user=["+user.getId()+"] name=["+user.getName()+"] location=["+user.getLocation()+"]");
}
}
}
The 1st SQL is what I expected. It is executed when crit.list() is called. On SQL level it returns the expected single row for Provider 0, User 1.
SELECT this_.id AS id43_1_,
this_.name AS name43_1_,
user1_.id AS id44_0_,
user1_.EX_PROVIDER_ID AS EX4_44_0_,
user1_.location AS location44_0_,
user1_.name AS name44_0_
FROM EX_PROVIDER this_
INNER JOIN EX_USER user1_
ON this_.id=user1_.EX_PROVIDER_ID
WHERE user1_.location=?;
However, this is not mapped to entity level as I expected. There, the restriction seems to affect the selection of the Provider only. When the user list is accessed, all users of the provider are read from DB neglecting the 'Berlin' restriction.
This was the same whether I used HQL, Hibernate Criteria (also with #Filter), JPA CriteriaBuilder.
SELECT exusers0_.EX_PROVIDER_ID AS EX4_43_1_,
exusers0_.id AS id1_,
exusers0_.id AS id44_0_,
exusers0_.EX_PROVIDER_ID AS EX4_44_0_,
exusers0_.location AS location44_0_,
exusers0_.name AS name44_0_
FROM EX_USER exusers0_
WHERE exusers0_.EX_PROVIDER_ID=?;
The log.
Criteria: provider=[0]
Criteria: user=[1] name=[User_2] location=[Berlin]
Criteria: user=[0] name=[User_1] location=[Munich]
I may achieve the expected result set using setResultTransformer(), but in this case the properly selected result is returned as some rows of entities.
#SuppressWarnings("unchecked")
private void demo() {
EntityManager em = null;
try {
em = emf.createEntityManager();
EntityTransaction tx = em.getTransaction();
try {
tx.begin();
Session session = (Session) em.getDelegate();
Criteria crit = session.createCriteria(ExProvider.class, "provider")
.createCriteria("exUsers", "user")
.add(Restrictions.eq("user.location","Berlin"))
.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);
;
List<ExProvider> providerList=(List<ExProvider>)crit.list();
logExProviderMapList(providerList);
tx.commit();
} finally {
if (tx!=null && tx.isActive()) tx.rollback();
}
} finally {
if (em!=null) em.close();
}
}
private void logExProviderMapList(List providerList) {
Iterator iter = providerList.iterator();
while ( iter.hasNext() ) {
Map map = (Map) iter.next();
ExProvider provider = (ExProvider) map.get("provider");
if(provider!=null) {
logger.info("Criteria: provider=["+provider.getId()+"]");
}
ExUser user = (ExUser) map.get("user");
if(user!=null) {
logger.info("Criteria: user=["+user.getId()+"] name=["+user.getName()+"] location=["+user.getLocation()+"]");
}
}
}
The SQL is the same as the 1st SQL above.
SELECT this_.id AS id43_1_,
this_.name AS name43_1_,
user1_.id AS id44_0_,
user1_.EX_PROVIDER_ID AS EX4_44_0_,
user1_.location AS location44_0_,
user1_.name AS name44_0_
FROM EX_PROVIDER this_
INNER JOIN EX_USER user1_
ON this_.id=user1_.EX_PROVIDER_ID
WHERE user1_.location=?;
The log.
Criteria: provider=[0]
Criteria: user=[1] name=[User_2] location=[Berlin]
My question was and is, whether it is possible to get this result as proper entity tree with Provider_A containing exactly the User from Berlin in its list.
Thanks again,
Wolfgang B