I have a one to many relationship. There is a problem in the way I
query for a B object. I was wondering what is the best way (most
efficient) to do that.
A a = new A("A");
B b = new B("B");
a.getBs().add(b);
pm.makePersistent(a); // it's done inside a transaction
A ap = pm.getObjectById(A.class, "A"); // FINE
B bp = pm.getObjectById(B.class, "B"); // NOT FOUND Exception
I guess B is not found because the real key is not B but B + A key.
How do you get the B object when you don't know nothing about A?
public class A {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk",
value = "true")
private String key;
@Persistent
@Extension(vendorName = "datanucleus", key = "gae.pk-name", value
= "true")
private String name;
@Persistent(mappedBy = "a")
private List<B> bs;
public A(String name) {
this.name = name;
bs = new ArrayList<B>();
}
... Getter/Setter
}
@PersistenceCapable(identityType =
javax.jdo.annotations.IdentityType.APPLICATION)
public class B {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk",
value = "true")
private String key;
@Persistent
@Extension(vendorName = "datanucleus", key = "gae.pk-name", value
= "true")
private String name;
@Persistent
private A a;
public B(String name) {
this.name = name;
}
... Getter/Setter
}
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