Hibernate version:2.1.6

Im trying to map the following construct:

A (1..1) -- (0..1) B

property accessors + constructors omitted for clarity:

class A()
{
int id;
B b;
}

class B()
{
int id;
A a;
}


Any single 'A' could contain 0 or 1 'B'.
'B' cannot exist without an associated 'A'.

Ive been trying to use many-to-one and one-to-one, but when I try and save an 'A' I keep getting:

PropertyValueException : not-null property references a null or transient value: test.B.a

I have a simple main() that does this:

A a1 = new A();
B b = new B();
a1.setB( b );

A a2 = new A();

session.save( a1 );
session.save( a2 );

Since the lifetime of 'B' is controlled by 'A', I considered that A is the parent, B is the child in this mapping.

Can I map this using two tables, and not having a Set<B> in class A?



Nick

Ok, ignore this, Ive figured it out - the mapping i had was fine - I was simply not setting the A on B and B on A.

Can you send me your example? I'm struggling with the same thing, and cannot the save to cascade down to the child.


I create the parent, then the child, call the setter, and then call save,
and it will only insert the parent.

A.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<!--$Id$ -->

<hibernate-mapping package="test">

<class name="A" table="A_rtab" >

<id name="id" type="long" column="id" unsaved-value="0" >
<generator class="native"/>
</id>

<one-to-one name="b"
property-ref="a"
cascade="save-update"
/>

</class>

</hibernate-mapping>


B.hbm.xml


<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping package="test">

<class name="B" table="B_rtab" >

<id name="id" type="long" column="id" unsaved-value="0" >
<generator class="native"/>
</id>

<property name="name"/>

<many-to-one
name="a"
column="A_ID"
class="A"
not-null="true"
unique="true"
/>

</class>

</hibernate-mapping>




Dont forget to link both ways:

A a = new A(); // Parent
B b = new B(); // Child

a.setB( b );
b.setA( a );

session.save( a );

if you just do this:

A a = new A(); // Parent
B b = new B(); // Child

a.setB( b );

you will get a nont-null property execption when you attempt to cascade the save.

Nick

You're using a many-to-one in your mapping. I'm attempting to do a one-to-one in both directions, but can never get it to insert the child, unless i do it explicitly. The cascade doesn't seem to work , as it seems to be trying to insert the child first.

Its not many to many, its:
(1..1) -- (0..1)

Notice the unique="true"

Nick

Now, my only problem is how to delete the old instance of B when you create a new B, and set it on A.