Best Practices: Howto cache instead of long transaction

daniel.frey · **Joined:** Thu Jun 17, 2004 6:31 am **Posts:** 5

Hi

I'd like to use Hibernate for the following UseCase: A user does some manipulations on business objects, and when he saves the work, the BOs are made persistent to the DB.

Strategy 1: At the beginning I start a transaction, and when the user saves, I commit the whole stuff and start a new transaction. The disadvantage of this is that a user might take a cup of coffee and the chances of a cuncurrent update increase.

Strategy 2: I cache the modified/create/deleted BOs and flush them during one short transaction. The bad thing about this is I have to invent caching strategies once more.

I am implementing this as a desktop application, so both strategies can be taken into account. Which one is the one recommended by you? Reasons?

Thanks for your advice
Daniel Frey

anthony · **Posted:** Fri Jul 16, 2004 2:57 pm

---- Session A opened beginTrans ---------
1- get objects
---- Session A closed and committed-------
---- Objects are detached -------
2- show these object in your UI
3- user modifies objects
---- Session B opened beginTrans
4- reattached objects with new session
5- do some version check
6- (flush)
---- session B closed and committed --------

this is only one solution

you can also store somewhere (httpSession?) the hibernate session and it live a long time and use disconnect/reconnect...

read reference guide, it is explained

http://www.hibernate.org/hib_docs/refer ... g-detached
http://www.hibernate.org/hib_docs/refer ... tions.html

daniel.frey · **Joined:** Thu Jun 17, 2004 6:31 am **Posts:** 5

Thanks, Anthony, your answer shows that I am on the right way, as this is exactly what I am doing at the moment. More precisely:

1-Session A: get objects
2-Session A: show these object in your UI
3-No Session: user modifies objects: I keep track of all modified/updated and deleted objects.
4-Session B: reattached objects with new session: I use saveOrUpdate
5-Session B: do some version check: My config contains a timestamp property
6-Session B: (flush): dito

However, I get strange exceptions, so I was doubting whether I adopted the right strategy. The exception is:

Code:

[ERROR] JDBCException: 38 could not delete collection rows: [IFEntry.parents#121]
java.sql.SQLException: Try to insert null into a non-nullable column: column: CHILD_ID table: ENTRY_ENTRY in statement [update ENTRY_ENTRY set CHILD_ID=null where CHILD_ID=? and PARENT_ID=? and CHILD_ID=?]
   at org.hsqldb.jdbc.jdbcUtil.throwError(Unknown Source)
   at org.hsqldb.jdbc.jdbcPreparedStatement.executeUpdate(Unknown Source)
   at net.sf.hibernate.impl.NonBatchingBatcher.addToBatch(NonBatchingBatcher.java:22)
   at net.sf.hibernate.collection.AbstractCollectionPersister.deleteRows(AbstractCollectionPersister.java:566)
   at net.sf.hibernate.impl.ScheduledCollectionUpdate.execute(ScheduledCollectionUpdate.java:47)
   at net.sf.hibernate.impl.SessionImpl.executeAll(SessionImpl.java:2414)
   at net.sf.hibernate.impl.SessionImpl.execute(SessionImpl.java:2370)
   at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2236)
   at net.sf.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:61)
   at BusinessDelegate.saveAll(BusinessDelegate.java:118)
   at SaveAction.actionPerformed(SaveAction.java:32)

That happens when I am updating (updateOrSave) an existing DefaultEntry object (implements IFEntry):

Code:

DefaultEntry@107bd0d[
    work=<null>,
    timestamp=2004-07-16 21:18:43.845,
    id=121,
    children=[],
    parents=[
        EntryConnector@13dd8[
            rank=0,
            EntryConnectorId@18353cf[
                parent=188,
                child=121
            ],
            timestamp=2004-07-16 23:39:05.745
        ]
    ],
]

which has a relation to the EntryConnector (-> ENTRY_ENTRY table). Hibernate tries to update this dependent object too and wants to set one part of the primary key (CHILD_ID -> child=121) of ENTRY_ENTRY to null, which invokes the exception. I don't see why this is necessary, it should only update the DefaultEntry, not the EntryConnector. And if it updates the EntryConnector, then why setting this half-PK to null? Can I configure it to not do that?

I've got a simple two-tables ERD, representing a graph.

Code:

CREATE TABLE ENTRY (
    ID IDENTITY,
    TIMESTAMP TIMESTAMP,
    ...
);
CREATE TABLE ENTRY_ENTRY (
    PARENT_ID INTEGER,
    CHILD_ID INTEGER,
    TIMESTAMP TIMESTAMP,
    RANK INTEGER,
    PRIMARY KEY (PARENT_ID, CHILD_ID)
);

and the row being updated is of the ENTRY table. I debuged throu the process and the ENTRY row is updated ok, but the dependent collection fails (the ENTRYs are dependent on the connection table ENTRY_ENTRY). Here's the config:

Code:

<hibernate-mapping package="">
    <class name="IFEntry" table="ENTRY">
        <id name="id" type="integer" unsaved-value="null">
            <generator class="identity"/>
        </id>
        <discriminator column="discriminator"/>
        <timestamp name="timestamp"/>
        ...
        <set name="children" table="ENTRY_ENTRY" inverse="true">
            <key column="PARENT_ID"/>
            <one-to-many class="EntryConnector"/>
        </set>
        <set name="parents" table="ENTRY_ENTRY">
            <key column="CHILD_ID"/>
            <one-to-many class="EntryConnector"/>
        </set>
        <subclass name="DefaultEntry" discriminator-value="default"/>
    </class>
</hibernate-mapping>

<hibernate-mapping package="">
    <class name="EntryConnector" table="ENTRY_ENTRY">
        <composite-id name="id" class="EntryConnectorId">
            <key-many-to-one name="parent" class="IFEntry" column="parent_id"/>
            <key-many-to-one name="child" class="IFEntry" column="child_id"/>
        </composite-id>
        <timestamp name="timestamp"/>
        <property name="rank" type="integer"/>
    </class>
</hibernate-mapping>

I am using HSQLDB 1.7.2rc6 and my code in the session (B) is:

Code:

public static void saveAll() {
    try {
        final Session session = HibernateUtils.currentSession();
        final Transaction tx = session.beginTransaction();
        for (Iterator iterator = cacheToDelete.iterator(); iterator.hasNext();) {
            final Object o = iterator.next();
            System.out.println("deleting: " + o);
            session.delete(o);
        }
        for (Iterator iterator = cacheToSave.iterator(); iterator.hasNext();) {
            final Object o = iterator.next();
            System.out.println("saving  : " + o);
            session.saveOrUpdate(o);
        }
        tx.commit();
        HibernateUtils.closeSession();
    }
    catch (HibernateException e) {
        e.printStackTrace();
        throw new IllegalStateException("Error during save");
    }
}

Thanks for any idea or advice.
Daniel Frey