Hi.
I got tree classes that has one-to-many relationship with each other.
A has a child class B (one to many)
B has a child class C(one to many)
@PersistenceCapable
class A {
@PrimaryKey
@Persistent
public Key key;
@Persistent(mappedBy = "a")
@Element(dependent = "true")
public List<B> bList = new ArrayList<B>();
}
@PersistenceCapable
class B {
@PrimaryKey
@Persistent
public Key key;
@Persistent(mappedBy = "b")
@Element(dependent = "true")
public List<C> cList = new ArrayList<C>();
@Persistent
public A a;
}
@PersistenceCapable
class C {
@PrimaryKey
@Persistent
public Key key;
@Persistent
public B b;
}
and here is my sample code. code does following steps
1)Create an A instance and persist it if it does not exist in
datastore
2)get A from DB and add B to its list
3) get B from DB and add C to its list
4) delete B and C from DB
PersistenceManager pm = PMF.get().getPersistenceManager();
A a = null;
B b = null;
C c = null;
//1)If A does not exist persist A
try{
a = pm.getObjectById(A.class,"A");//check if A exist
}catch(Exception e){
try {
pm.currentTransaction().begin();
a = new A();
a.key = new
KeyFactory.Builder(A.class.getSimpleName(),"A").getKey();
pm.makePersistent(a);
pm.currentTransaction().commit();
log.info("New a was created");
} finally {
if(pm.currentTransaction().isActive())
pm.currentTransaction().rollback();
}
}
log.info("id of a is " + a.key);
//2)get A from DB and add B to its list
try {
pm.currentTransaction().begin();
A newA = pm.getObjectById(A.class,"A");
b = new B();
b.key = new
KeyFactory.Builder(newA.key).addChild(B.class.getSimpleName(),
"B").getKey();
newA.bList.add(b);
pm.currentTransaction().commit();
log.info("New b was created");
} finally {
if(pm.currentTransaction().isActive())
pm.currentTransaction().rollback();
}
log.info("Key of b " + b.key);
//3) get B from DB and add C to its list
pm.currentTransaction().begin();
try {
Key bKey = new
KeyFactory.Builder(A.class.getSimpleName(),
"A").addChild(B.class.getSimpleName(), "B").getKey();
B newB =
pm.getObjectById(B.class,bKey);//<----------Error we
cannot retrieve B
c = new C();
c.key = new
KeyFactory.Builder(newB.key).addChild(C.class.getSimpleName(),
"C").getKey();
newB.cList.add(c);
pm.currentTransaction().commit();
log.info("New c was created");
} finally {
if(pm.currentTransaction().isActive())
pm.currentTransaction().rollback();
}
//4) delete B and C from DB
pm.currentTransaction().begin();
try {
C newC = pm.getObjectById(C.class,c.key);
pm.deletePersistent(newC);
B newB = pm.getObjectById(B.class,b.key);
pm.deletePersistent(newB);
pm.currentTransaction().commit();
log.info("b and c was deleted");
} finally {
if(pm.currentTransaction().isActive())
pm.currentTransaction().rollback();
}
first time I run this code it works. here is my log messages
INFO: New a was created
INFO: id of a is A("A")
INFO: New b was created
INFO: Key of b A("A")/B("B")
INFO: New c was created
INFO: b and c was deleted
it creates a new A , B and C then in step 4 it deletes B and C
when I run it second time I get following an error message
javax.jdo.JDOObjectNotFoundException: Could not retrieve entity of
kind B with key A("A")/B("B")
Problem is, if my parent(A) is already in datastore I cannot add a new
child(B).
I dont get any error at step2. It seems like B is persisted correctly
but when I try to retrive it at step 3( with code
"pm.getObjectById(B.class,bKey)" at line 3 of this step)
I cannot retrieve it. and when I check it from admin console I see
that it is not persisted.
I found this post which says that I have to assign primary keys by
hand but it still does not work.
http://groups.google.com/group/google-appengine-java/browse_thread/thread/22e808b07fd93062/e81ec52c4fee8103?lnk=gst&q=owned+one+to+many#e81ec52c4fee8103
any help would be appreciated. thanks
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