JPA Nullable JoinColumn - jpa

Question

I have an entity:
public class Foo {
#Id
#GeneratedValue
private Long id;
private String username;
#ManyToOne(cascade = { CascadeType.MERGE }, fetch = FetchType.LAZY, optional = true)
#JoinColumn(name = "ParentID", nullable = true)
private Foo parent;
// other fields
}
With this kind of relationship, each Foo object has a parent, except the first Foo instance in the DB which has a NULL ParentID. When i try to create a query via criteria api and try to search for the first Foo object (null parent id) using any of it's properties (ID, username etc..), i get a:
javax.persistence.NoResultException: No entity found for query
How should the JoinColumn be implemented in this case? How should i get the first Foo object in the DB which has a null parent ID?
Thanks
Updated September 28 2011
What i am trying to achieve is to look lookfor all Foos with a username starting in "foo" and would like to use as separate object being returned then:
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder;
CriteriaQuery<FooDto> criteriaQuery = criteriaBuilder.createQuery(FooDto.class);
Root<Foo> foo = criteriaQuery.from(Foo.class);
criteriaQuery.multiselect(foo.get("id"), foo.get("username"), foo.get("parent").get("username"), foo.get("property1")
//other selected properties);
Predicate predicate = criteriaBuilder.conjunction();
predicate = criteriaBuilder.and(predicate, criteriaBuilder.like(foo.get("username").as(String.class), criteriaBuilder.parameter(String.class, "username")));
// other criteria
criteriaQuery.where(predicate);
TypedQuery<FooDto> typedQuery = entityManager.createQuery(criteriaQuery);
typedQuery.setParameter("username", "foo%");
// other parameters
// return result
assuming that the usernames are foo1, foo2 and foo3 wherein foo1 has a null parent, the result set will only return foo2 and foo3 even if the foo1 has a username that starts with the specified predicate.
and also searching for foo1 alone will throw a
javax.persistence.NoResultException: No entity found for query
Is there a way to still include foo1 with the rest of the results? or foo1 will always be a special case since i have to add a criteria specifying that the parent is null? Or perhaps ai have missed an option in the joinColumn to do so.
Thanks
UPDATED Thu Sep 29 13:03:41 PHT 2011
#mikku
I have updated the criteria part of the post above (property1), because i think this is the part that is responsible for foo1 not to be included in the Result Set.
Here's a partial view of the generated query from the logs:
select
foo.id as id,
foo.username as username,
foo.password as password,
foo.ParentID as parentId,
foo_.username as parentUsername,
foo.SiteID as siteId,
from FOO_table foo, FOO_table foo_ cross join Sites site2_
where foo.ParentID=foo_.id and foo.SiteID=site2_.id and 1=1
and foo.username=? and site2_.remoteKey=? limit ?
and this wont return Foo1, obviously because username value is from foo_ which is why my original question is 'how should i get to Foo1'.
On the part that i have commented that ill use SelectCase and mix it up with your first reply, what i did is to add this part on the multiselect:
criteriaBuilder
.selectCase()
.when(criteriaBuilder.isNotNull(agent.get("parent")), agent.get("parent").get("username"))
.otherwise(criteriaBuilder.literal("")),
replacing the
foo.get("parent").get("username")
However this wont be able to get Foo1 as well. My Last resort though inefficient would probably check if the parameters are of Foo1 and create a criteriaQuery specifying a literal value for username, and using the default query otherwise.
Suggestions/alternatives are very much appreciated.

Answer 1

EDIT:
In your edited question nullable joincolumn is not problem - missing construction of FooDto, multiselect etc are. You can achieve your goal with following:
Querying:
/**
* Example data:
* FOO
* |id|username|property1|parentid|
* | 1| foo | someval| null|<= in result
* | 2| fooBoo | someval2| 1|<= in result
* | 3|somename| someval3| null|
*/
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<FooDto> c = cb.createQuery(FooDto.class);
Root<Foo> fooRoot = c.from(Foo.class);
Predicate predicate = cb.like(fooRoot.get("username").as(String.class),
cb.parameter(String.class, "usernameParam"));
c.select(
cb.construct(FooDto.class,
fooRoot.get("id"),
fooRoot.get("username"),
fooRoot.get("property1")))
.where(predicate);
TypedQuery<FooDto> fooQuery = em.createQuery(c);
fooQuery.setParameter("usernameParam", "foo%");
List<FooDto> results = fooQuery.getResultList();
Object to hold data:
public class FooDto {
private final long id;
private final String userName;
private final String property1;
//you need constructor that matches to type and order of arguments in cb.construct
public FooDto(long id, String userName, String property1) {
this.id = id;
this.userName = userName;
this.property1 = property1;
}
public long getId() { return id; }
public String getUserName() { return userName; }
public String getProperty1() { return property1; }
}