JPA manyToMany not persisting in assocation table - spring

Question

I'm trying the following unit test:
#Test
#Transactional
public void thatFolderLocationAssociationTableIsWorking() {
Location l1 = new DomesticLocation();
l1.setDeptName("Test name 1");
Location l2 = new DomesticLocation();
l2.setDeptName("Test name 2");
KMLFolder k1 = new KMLFolder();
k1.setName("Test name 1");
KMLFolder k2 = new KMLFolder();
k1.setName("Test name 2");
List<Location> locations = new ArrayList<Location>();
locations.add(l1);
locations.add(l2);
k1.setLocations(locations);
kmlFolderServiceImpl.save(k1);
assertEquals("Test name 1", kmlFolderServiceImpl.find(1L).getLocations().get(0).getDeptName());
assertEquals("Test name 2", kmlFolderServiceImpl.find(1L).getLocations().get(1).getDeptName());
//The following line gets the NPE
assertEquals("Test name 1", locationServiceImpl.find(1L).getKmlFolderList().get(0).getName());
}
I'm getting NPEs on the laster assertions where I'm trying to retrieve KMLFolder.getName() from the Locations The other assertions are working, where I get the Location name from the KMLFolder.
Here are my JPA definitions:
#ManyToMany(mappedBy="kmlFolderList", cascade=CascadeType.ALL)
private List<Location> locations = new ArrayList<Location>();
#ManyToMany
#JoinTable(name="LOCATION_KMLFOLDER",
joinColumns={#JoinColumn(name="KMLFOLDER_ID", referencedColumnName="ID")},
inverseJoinColumns={#JoinColumn(name="LOCATION_ID", referencedColumnName="ID")}
)
The appropriate table is being created when I run the test. Here's the console output:
Hibernate:
create table project.LOCATION_KMLFOLDER (
KMLFOLDER_ID bigint not null,
LOCATION_ID bigint not null
) ENGINE=InnoDB
...
Hibernate:
alter table project.LOCATION_KMLFOLDER
add index FK_lqllrwb2t5cn0cbxxx3ms26ku (LOCATION_ID),
add constraint FK_lqllrwb2t5cn0cbxxx3ms26ku
foreign key (LOCATION_ID)
references project.KMLFolder (id)
Hibernate:
alter table .LOCATION_KMLFOLDER
add index FK_ckj00nos13yojmcyvtefgk9pl (KMLFOLDER_ID),
add constraint FK_ckj00nos13yojmcyvtefgk9pl
foreign key (KMLFOLDER_ID)
references project.Locations (id)
The console does not show inserts in to the LOCATION_KNLFOLDER table as I expect. Any thoughts on why this may be happening?

Answer 1

You're initializing the inverse side of the association, that Hibernate ignores, instead of (or in addition to) initializing the owner side of the association, that Hibernate doesn't ignore.
The owner side is the side without the mappedBy attribute.