Using CriteriaBuilder to select entities referenced by refTable - jpa

Question

I'm very new to JPA (based on eclipselink) so be patient with me and my question. I found JPA is an elegant way to handle simple DB statements. But, now I'd like to do some more complicated task.
So let me explain what I want: I've got a table holding person data (lets say the persons name). In an other table I'd like to keep address lists. Because a person way part of several adresslists and one adress list may keep several persons I need an ref-table jo join these collections.
So my DB-tables look like this:
SQL (not exact DDL syntax but it helps to understand!) --without constraints etc
--the person keeps data of persons
CREATE TABLE a_person
(
oid serial PrimaryKey NOT NULL,
vorname character varying(50),
nachname character varying(50) NOT NULL
--
)
--the adresslist is quite simple: just a name of the list is storred
CREATE TABLE a_adressliste (
(
oid serial PrimaryKey NOT NULL,
label character varying(25) NOT NULL
--<more collumns here>
)
--the table refering the list the the containing persons
CREATE TABLE a_listen_person
(
fk_adressliste bigint PrimaryKey NOT NULL, --ref to a_person.oid
fk_person bigint PrimaryKey NOT NULL, --ref to a_adressliste.oid
)
Having this structure and some data in the DB it's easy to select the adress lists using the following SQL statement:
select * from a_person p where p.oid in (
select
lp.fk_person
from
a_listen_person lp, a_adresssliste al
where
lp.fk_adressliste = al.oid AND al.label = {LISTE_LABEL}
)
Now, According tho the structure within the DB, I've got the corresponding JAVA POJO's to these tables (I've skipped the annotations to keep my code a little shorter)
JAVA
public class Person implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "oid")
private Integer oid;
private String vornmae;
private String nachname;
//getter; setter and the other missing stuff...
}
public class Adressliste implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "oid")
private Integer oid;
private String label;
}
public class ListenPerson implements Serializable {
#EmbeddedId
private ListenPersonPK listenPerson;//build from Person.oid and Adressliste.oid
private Person person;
private Adressliste adresssliste;
//getter; setter and the other missing stuff...
}
Now I've written a finder method in JAVA where I use a CriteriaBuilder to filter the entities by several attributes (according to the Person POJO). But I did not manage to select the Person according to a given list name.
By now my method looks like this:
public TypedQuery<Person> prepareQueryFiltered(Filter filter) {
TypedQuery<Person> retVal;
EntityManager em = this.getEntityManager();
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<Person> query = builder.createQuery(Person.class);
Root<Person> cust = query.from(Person.class);
query.select(cust);
List<Predicate> predicateList = new ArrayList<Predicate>();
Predicate predicate;
if (null != filter.getVorname()) {
predicate = builder.like(
builder.lower(cust.<String>get("vorname")),
"%" + filter.getVorname().toLowerCase() + "%");
predicateList.add(predicate);
}
if (null != filter.getNachname()) {
predicate = builder.like(
builder.lower(cust.<String>get("nachname")),
"%" + filter.getNachname().toLowerCase() + "%");
predicateList.add(predicate);
}
//some more filtered attributes ...
query.where(predicateList.toArray(new Predicate[predicateList.size()]));
retVal = em.createQuery(query);
return retVal;
}
As you can imagine the filter attribute keeps all the data to filter my entities with. But how does the code look like if I'd like to get all the person entities belonging to a given list name?
I started to use 'Subquery's but I did not get the correct syntax. Could you please give me some hints?

Answer 1

For examples of sub-queries in the Criteria API see,
http://en.wikibooks.org/wiki/Java_Persistence/Criteria#Subquery
Also, I don't think you need a sub-query, a simple join should work.
Select p from Person p, ListenPerson l where l.person = p and l.adresssliste.label = :label