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failing to retrieve a collection

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gromit

Post subject: failing to retrieve a collection

Posted: Tue Jul 13, 2004 3:48 pm

Newbie

Joined: Tue Jul 13, 2004 3:25 pm
Posts: 4
Location: M

i'm new with hibernate (and spring), i am having troubles trying to retrieve
a collection (defined as lazy). Here is the relevant code:

Father.hbm.xml

Code:

    <!-- bi-directional one-to-many association to MapaConceptual -->
    <set
        name="children"
        lazy="true"
        inverse="true"
    >
        <key>
            <column name="idFather" />
        </key>
        <one-to-many
            class="Father"
        />
    </set>

Father.java

Code:

    public Set getChildren() {
        return this.children;
    }
    public void setChildren(Set children) {
        this.children = children;
    }

FatherDao.java

Code:

    Session session = SessionFactoryUtils.getSession(getSessionFactory(), false);
    try {
        session.lock(father, LockMode.NONE) ;
        java.util.Set set = father.getChildren() ;
        log.info("children.size = " + set.size()) ;

        return new java.util.ArrayList(set) ;

    } catch (HibernateException ex) {
        throw SessionFactoryUtils.convertHibernateAccessException(ex);
    }

a NullPointerException occurs in the println line, the children set is null, and i'm positive there is data associated with the given father.

please help! :)

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gromit

Post subject:

Posted: Tue Jul 13, 2004 3:59 pm

Newbie

Joined: Tue Jul 13, 2004 3:25 pm
Posts: 4
Location: M

i forgot to mention what the log output is:

Code:

50:18,906 DEBUG SessionImpl:1670 - reassociating transient instance: [Father#7]
50:18,906 DEBUG JDBCTransaction:82 - rollback
50:18,906 DEBUG SessionImpl:572 - transaction completion
50:18,906 DEBUG JDBCTransaction:103 - re-enabling autocommit
50:18,906 DEBUG SessionImpl:560 - closing session
50:18,906 DEBUG SessionImpl:3327 - disconnecting session
50:18,906 DEBUG SessionImpl:572 - transaction completion
java.lang.NullPointerException
        at FatherDao.getChildren(FatherDao.java:56)

please, note that immedialtly after the "reassociating transient instance" a rollback occurs, what could be going wrong at that point??

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VampBoy

Post subject:

Posted: Tue Jul 13, 2004 4:08 pm

Expert

Joined: Sat Jan 17, 2004 2:57 pm
Posts: 329
Location: In the basement in my underwear

Actually, the NullPointer occurs as soon as you call getChildren (according to the stacktrace). What does line 56 of your FatherDAO look like?

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gromit

Post subject:

Posted: Tue Jul 13, 2004 5:40 pm

Newbie

Joined: Tue Jul 13, 2004 3:25 pm
Posts: 4
Location: M

is the

Code:

log.info("children.size = " + set.size())

part :/

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gromit

Post subject:

Posted: Tue Jul 13, 2004 6:05 pm

Newbie

Joined: Tue Jul 13, 2004 3:25 pm
Posts: 4
Location: M

i have another collection associated and that is been fetched ok...

some part i din't mentioned is that Child is a subclass of other class, so at database level the idFather column doesn't exist in the Child table...
i'm affraid that is the problem but if so, how do i overcome it ??

the thing is, i want Father to have a collection of Child, not of the superclass of it, this are the table definitions:

Code:

Father              Thing            Child
------              ----------       ---------
id                  id               id        (PK FK that references Thing.id)
name                name             color
                    idFather

this is the mapping for Child in Thing.hbm.xml

Code:

<class name="Thing" table="thing" >

    <id name="id" type="int" unsaved-value="0" >
        <generator class="identity" />
    </id>

    <property name="name"  type="java.lang.String" not-null="true" />

    <!-- bi-directional many-to-one association to Usuario -->
    <many-to-one name="father" class="Father" not-null="true" >
        <column name="idFather" />
    </many-to-one>

    <joined-subclass name="Child" table="child" >
        <key column="id"/>
        <property name="name"  type="java.lang.String" not-null="true" />
    </joined-subclass>

</class>

thanks for your comments

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VampBoy

Post subject:

Posted: Tue Jul 13, 2004 7:45 pm

Expert

Joined: Sat Jan 17, 2004 2:57 pm
Posts: 329
Location: In the basement in my underwear

gromit wrote:

is the

Code:

log.info("children.size = " + set.size())

part :/

Oops, silly me :(

I'm tired and my brain hurts. What threw me off is that if we lazy load a collection and nothing is found it just returns an empty collection.

However, this

<one-to-many
class="Father"
/>

doesn't look right in the Father.hbm.xml, shouldn't the class be Thing or Child (you decide :))

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