Lazy one-to-one, revisited

diz · **Joined:** Fri Jul 16, 2004 4:43 am **Posts:** 3

Hello all,
Before I get started I should probably mention that I am well aware of
http://www.hibernate.org/162.html, the hibernate manual and I have spent the last two days reading this forum.

As the subject suggests, I am unable to get lazy loading from a one-to-one mapping.
I have two relatively simple clases in a one-to-one relationship with each other. Everything seems to be set up fine:

Now for the details:

BlobItemPayload

lazy

BlobItem

The entire process of creating and reading objects works flawlessly (no abnormal messages in the log) but whenever I call .list and get a list of BlobItem objects, hibernate goes ahead and does a select for each of them in order to retrieve the associated BlobItemPayload.

I am using the following:

J2SDK 1.4.1_02
Any ideas/hints would be greatly appreciated.

Best regards,
diz

The actual mapping is as follows:

Code:

<hibernate-mapping>
    <class        name="com.aspectcapital.util.timeseries.hibernate.BlobItemPayload"
        table="BlobData" dynamic-update="false"
        dynamic-insert="false"  select-before-update="false"
        lazy="true">

        <id name="payload_id" column="payload_id" type="long" >
            <generator class="native"> </generator>
        </id>

        <property .../SNIP/...   />

        <one-to-one
            name="payload_info"
            class="com.aspectcapital.util.timeseries.hibernate.BlobItem"
            cascade="none" outer-join="false" constrained="false" />
    </class>
</hibernate-mapping>

Code:

<hibernate-mapping>
    <class  name="com.aspectcapital.util.timeseries.hibernate.BlobItem"
        table="BlobItems"  dynamic-update="false"                           dynamic-insert="false" select-before-update="false" lazy="true" >

        <id name="item_id" column="item_id" type="long">
            <generator class="foreign">
                <param name="property">payload</param>
            </generator>
        </id>

        <property
          ... /SNIP/ ...>

        <one-to-one name="payload" constrained="true" />
    </class>
</hibernate-mapping>

[/list]

emmanuel · **Posted:** Fri Jul 16, 2004 10:14 am

Hum, not sure but a foreign generated identifier might break the lazy capability.

diz · **Joined:** Fri Jul 16, 2004 4:43 am **Posts:** 3

Emmanuel,

What do you think I should use instead? I cannot define an ID without a generator (hibernate doesn't allow that).

I have also attempted to use different types of generators, explicitly (increment, hilo, assigned) without any luck.

Did anyone manage to create a lazy a one-to-one similar to mine?

Best regards,
diz

emmanuel · **Posted:** Fri Jul 16, 2004 10:28 am

If assigned failed, then there is another problem somewhere. You somehow access BlobItemPayload

diz · **Joined:** Fri Jul 16, 2004 4:43 am **Posts:** 3

emmanuel wrote:

If assigned failed, then there is another problem somewhere. You somehow access BlobItemPayload

Unfortunatelly, this is not the case. All the queries are genrated by one statement only:

Code:

List items = session.find("from com....BlobItem as b");

The queries generated look like this:

Code:

Hibernate: select blobitem0_.item_id as item_id, blobitem0_.start_timestamp as start_ti2_, blobitem0_.end_timestamp as end_time3_, blobitem0_.entries as entries from BlobItems blobitem0_
Hibernate: select blobitempa0_.payload_id as payload_id0_, blobitempa0_.timeseries_data as timeseri2_0_ from BlobData blobitempa0_ where blobitempa0_.payload_id=?
Hibernate: select blobitempa0_.payload_id as payload_id0_, blobitempa0_.timeseries_data as timeseri2_0_ from BlobData blobitempa0_ where blobitempa0_.payload_id=?
.... and so on, one for each BlobItem

Since the last message, I have also attempted to use assigned ids for both ends of the relationship (no foreign generator). It didn't make any difference. :-(

Are there any other ways to obtain the lazy loading? I could, of course save the id of one object manually in the other object and handle all loading/saving by hand. But that pretty much defeats the point of using Hibernate.

Regards,
diz

amezick · **Joined:** Mon Nov 03, 2003 11:48 pm **Posts:** 29

Been trying to do the same thing. See the following links:
http://opensource.atlassian.com/project ... se/HB-1093
http://forum.hibernate.org/viewtopic.ph ... highlight=
http://forum.hibernate.org/viewtopic.ph ... highlight=
http://forum.hibernate.org/viewtopic.ph ... highlight=

As you can see, your setup isn't going to work. It looks like we are going to have to drop the foreign generation on the child for something else and then use many-to-one for the mapping. Still playing with test code to try and firgure out another way.