one to many - JPA+EclipseLink - Move entities in a @OneToMany relationship -

my implementation of onetomany relationsship in description:

http://en.wikibooks.org/wiki/java_persistence/onetomany

entity group:

@entity public class group {  @onetomany(cascade = { cascadetype.all }, orphanremoval = true) private list<unit> units = new arraylist<unit>();   public void addunit(unit unit) {     this.units.add(unit);     if (unit.getgroup() != this) {         unit.setgroup(this);  } } 

entity unit:

@entity public class unit {  @manytoone(cascade = cascadetype.persist) private group group;  public void setgroup(group group) {     this.group = group;     if (group != null && !group.getgooditems().contains(this)) {         group.getgooditems().add(this);     }  } } 

now want move 1 unit between 2 groups with:

unit.setgroup(group2);

after operation can see in database in relation table group_unit unit related group1 , group2.

how can move unit between 2 groups correctly?

you should add mappedby in annotation:

@onetomany(cascade = { cascadetype.all }, orphanremoval = true, mappedby="group") private list<unit> units = new arraylist<unit>(); 

with mappedby not need join_table anymore.