another Parent/Child Problem (sorry)

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

Hy,

I'm trying to persist 2 classes Parent and Child:
class Parent{
private String id;
private Child myPreferedChild;
private String name;
//getters and setters
}

class Child{
private String id;
private Parent myOnlyParent;
private String name;
//geters and setters
}

For the moment, there is no one-to-many relation between parent and childrens (the parent only knows its prefered child).

In the model, there is one table for each class.
A parent HAS obligatory a prefered child (the column is not nullable).
The child may not have a Parent (the column is nullable)

I used two relation "many-to-one" with cascade="all".
I used not-null="true" on the parent->child relationship and not-null="false" on the child->parent relationship.

A use case is to create a child that have a Parent that is not already in the database.
So the code is like :
Child myNewChild = new Child();
myNewChild.setName("newChild");
Parent myParent = new Parent();
myParent.setName("new parent");
myParent.setPreferedChild(myNewChild);
myNewChild.setParent(myParent);

//persist the child
session.save(myNewChild);

When I do this, the error is that hibernate is trying to save the Parent first and I get an exception saying that the PREFERED_CHILD_ID cannot be NULL.

Is there anyone who could help me for this ?

Thanks
joe

dimas · **Posted:** Wed Dec 03, 2003 6:01 am

What is value fro "inverse" attribute for both mappings?

Or just show the mapping...

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

Here is the mapping :

Code:

    <class
        name="Child"
        table="CHILD"
        dynamic-update="false"
        mutable="true"
    >

        <id
            name="id"
            column="ID"
            type="java.lang.Long"
            unsaved-value="null"
        >
            <generator class="sequence">
                <param name="sequence">CHILD_SEQ</param>
            </generator>
        </id>

        <many-to-one
            name="parent"
            class="Parent"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="PARENT_ID"
            not-null="false"
        />

        <property
            name="activityCode"
            type="java.lang.String"
            update="true"
            insert="true"
            column="NAME"
        />
</class>


    <class
        name="Parent"
        table="Parent"
        dynamic-update="true"
        mutable="true"
    >

        <id
            name="id"
            column="ID"
            type="java.lang.Long"
            unsaved-value="null"
        >
            <generator class="sequence">
                <param name="sequence">PARENT_SEQ</param>
            </generator>
        </id>

        <property
            name="name"
            type="java.lang.String"
            update="true"
            insert="true"
            column="NAME"
        />

        <many-to-one
            name="preferedChild"
            class="Child"
            cascade="all"
            outer-join="auto"
            update="true"
            insert="true"
            column="PREFERED_CHILD_ID"
            not-null="true"
        />

    </class>

[/code]

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

I am actually trying some combinations for the attributes "cascade" to call explicitly save() on the child, then on the parent...

dimas · **Posted:** Wed Dec 03, 2003 6:46 am

Since cascade="none" for the Child's parent property, when you save child, Hibernate will not save its parent automatically.

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

Yeah, I know, but as I was saying, I'm currently modifying it.
For the moment, I resolve It by saying that the preferedChild is just a Long object that I set myself.

Thanks
joe

dimas · **Posted:** Wed Dec 03, 2003 7:10 am

I think you need to mark one of the ends of your bi-directional relationship as "inverse" end.

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

I don't think so, because, here it's not real Bi-directionnal relations.
It is just 2 many-to-one relations, on which you cannot put the attribute inverse="true".

Anyway, I obtain something working, so it's OK for me.
I'm still working on it....

Thanks for your responses

Joe

dimas · **Posted:** Wed Dec 03, 2003 7:25 am

Oh sorry, you are right - "inverse" is not available for many-to-one.

Don't you think one-to-one is better suited for your needs?

joel1di1 · **Joined:** Wed Sep 03, 2003 4:59 am **Posts:** 12

I don't think so, There is no link between the parent id and the child id...

emmanuel · **Posted:** Wed Dec 03, 2003 9:19 am

In hibernate 2.1 you can use the property-ref attribute in one-to-one.

gavin · **Posted:** Wed Dec 03, 2003 9:44 am

correct, as Emmanuel says, use a <one-to-one> with a property-ref.