Manipulating lists and index problem!

mgoulene · **Joined:** Thu Oct 23, 2003 10:55 am **Posts:** 11

Hi all,

It seems that I misundertood how the transparent persistent collection (managed by reachability) worked with Hibernate.
Here is a sample configuration hbm file with a bidirectionnal Parent-Child relationship:

Code:

<class name="com.oalia.apps.purchaser.bo.common.nomenclature.NomenclatureItem" table="NOMENCLATURE_ITEM"
        dynamic-update="false"
        dynamic-insert="false"
        discriminator-value="1">

        <id name="id" column="ID" type="java.lang.Long" unsaved-value="null">
            <generator class="native"/>
        </id>
        <property
            name="name"
            type="java.lang.String"
            update="true"
            insert="true"
            column="NAME"
            not-null="false"
            unique="false"
        />

        <property
            name="rank"
            type="java.lang.Integer"
            update="true"
            insert="true"
            column="RANK"
            not-null="false"
            unique="false"
        />

        <many-to-one
            name="nomenclature"
            class="com.oalia.apps.purchaser.bo.common.nomenclature.Nomenclature"
            cascade="none"
            outer-join="auto"
            update="false"
            insert="false"
            column="NOMENCLATURE_ID"
            not-null="true"
        />

    </class>
    <class name="com.oalia.apps.purchaser.bo.common.nomenclature.Nomenclature"
        table="NOMENCLATURE"
        dynamic-update="false"
        dynamic-insert="false">

        <id name="id" column="ID" type="java.lang.Integer" unsaved-value="null">
            <generator class="native"/>
        </id>

        <list name="items" lazy="false" inverse="true" cascade="all">
              <key column="NOMENCLATURE_ID"/>
              <index column="RANK"/>
              <one-to-many class="com.oalia.apps.purchaser.bo.common.nomenclature.NomenclatureItem"/>
        </list>
        <property
            name="name"
            type="java.lang.String"
            update="true"
            insert="true"
            column="NAME"
            not-null="false"
            unique="false"/>
    </class>

The main problem is that index column and the represented child field (rank) are not updated. That means that:

Code:

nomenclature.getItems().add(new NomenclatureItem("n1"));
nomenclature.getItems().add(new NomenclatureItem("n2"));

the ranks are not set, and when retrieving the items in another session, the objects will not have the correct index.
The other problem is that the collection is not as persistent as it seams.
For instance:

Code:

Transaction tx = session.beginTransaction();
Nomenclature nomenclature = ... // Gets the nomenclature
NomenclatureItem ni = (NomenclatureItem)nomenclature.remove(3);
// The size of the items is n-1 in memory
tx.commit();
...
nomenclature = ... // Gets the same nomenclature
System.out.println(nomenclature.getItems().size()); // will display n !!!

Is there a mistake in the above code or is it a normal feature of the persistent indexed List?

Thanks in advance.

MG

emmanuel · **Posted:** Thu Oct 23, 2003 12:33 pm

1. as you said by the inverse="true", nomenclature item is responsible for link.
So nomenclatureItem.setNomenclature(nomenclature) is mandatory

2. lists can contains null objects and start from index 0, not 1.

mgoulene · **Joined:** Thu Oct 23, 2003 10:55 am **Posts:** 11

Sorry I would say:

Code:

nomenclature.addItem(new NomenclatureItem("n1")); 
nomenclature.addItem(new NomenclatureItem("n2"));

when addItem will do the two operation (setNomenclature and getItems().add()).

does anybody know a solution to automatically manage the item index (as a persistent list does...).

Thanks

emmanuel · **Posted:** Thu Oct 23, 2003 1:13 pm

Code:

<many-to-one
            name="nomenclature"
            class="com.oalia.apps.purchaser.bo.common.nomenclature.Nomenclature"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="NOMENCLATURE_ID"
            not-null="true"
        /> 

update=true, insert=true.

gavin · **Posted:** Thu Oct 23, 2003 1:48 pm

Quote:

does anybody know a solution to automatically manage the item index (as a persistent list does...).

No, it is virtually impossible to implement since Hibernate objects are not assumed to be always under the management of the container, and since we prefer to generate SQL at startup. We have discussed the difficulties with this many times before.

mgoulene · **Joined:** Thu Oct 23, 2003 10:55 am **Posts:** 11

Thanks a lot,

So to conclude, lets imagine that we have a persistent list managed with the index property like:

Code:

l = [o1, o2, o3, o4]

If in a transaction we are doing:

Code:

tx = session.gebeginTransaction();
l.remove(1); // here the list is [o1, o3, o4]
tx.commit()

When the next time we will retrieve the list it, will be

Code:

[o1, null, o3, o4]

That is different from before the commit...

Is that right?
So the list can not be considered as a Persistent List (as the JDO/ODMG specified)?

Thanks again

MG

gavin · **Posted:** Fri Oct 24, 2003 5:05 pm

Ummm Hibernate is not ODMG/JDO - it is much more powerful. (Hibernate supports detached instances, which is the reason for the difference).

And anyway if you use inverse="false" you will get the behaviour you just described.

Now, your snide tone is not appreciated and believe me I have spent much, much more time thinking about this problem than you, or anyone on the JDO or ODMG expert groups.

mgoulene · **Joined:** Thu Oct 23, 2003 10:55 am **Posts:** 11

Sorry about the tone,

* First of all I really appreciate the time you spend on answering my question (and as anyone on Hibernate - that is an extraordinary Persistent OR Binding Tool) .

* Believe me I did not try to be aggressive, I just wanted to understand how the things work. Please excuse me but my english is not as good as my french to explain this kind of things. I did not want to give a particular tone to my message (and not arrogant at all).

* I image you spend a lot of time thinking about this difficult problem. Let me say that I spend a lot of time too - I activelly participated in one of the first OR binding implementing ODMG in the first release, developped in Java for a customer called Sun (when I worked for O2 Tech.). I know this problem is difficult (as some others that are remarkably treated in Hibernate). I was just trying to understand the difference with the DList specification that are implemented by the Hibernate Persistent List and that are explicitly featured that point. You gave me the solution (inverse="false") and thanks a lot.

Sorry again and Thanks Gavin.

I hope we will have other discussions and I tried to spend time to make my messages kinder.

Mathieu

gavin · **Posted:** Sun Oct 26, 2003 4:27 pm

No problem :)