Re: Serialization of datacontext

[Andrus Adamchik]

Could you please open a bug report? We'll need to do some testing to  
settle on the best strategy (I am leaning towards not serializing the  
local DataRowStore at all, and rebuilding it on deserialization  
instead).

Thanks
Andrus
On Jun 4, 2007, at 11:46 AM, bob wrote:

Hi

I debugged this a bit and notice the following:

on DataContext serialization the following code is executed in  
writeObject(ObjectOutputStream)

        ...
        // Serialize local snapshots cache
        if (!isUsingSharedSnapshotCache()) {
            out.writeObject(objectStore.getDataRowCache());
        }
        ...

So if useSharedCache is false, the ObjectStore's DataRowStore is  
also serialized.

DataRowStore's reference to EventManager is transient and not  
serialized. So upon deserialization, when DataRowStore is read back  
in, the EventManager is null and this caused the exception below.

What is the best way to fix this? EventManager should not be  
transient? Or a new EventManager should be created in  
DataRowStore.readObject(ObjectInputStream)?

regards

bob

bob wrote:
Hi all
Using cayenne 1.2.3 and jdk 1.5 on Windows XP.
Sometimes while developing with Tomcat I get the following  
exception. Seems to happen on serialization of DataContext along  
with the session. Below the exception is a little test class to  
reproduce this. Note that if useSharedCache = true, then there is  
no exception. Should I open a JIRA issue or is this expected  
behavior?
Exception in thread "main"  
org.objectstyle.cayenne.CayenneRuntimeException: [v.1.2.3 May 6  
2007] Commit Exception
org.objectstyle.cayenne.access.DataContext.flushToParent 
(DataContext.java:1290)  
org.objectstyle.cayenne.access.DataContext.commitChanges 
(DataContext.java:1166) test.SerializeDCTest.main 
(SerializeDCTest.java:29)
Caused by: java.lang.NullPointerException
org.objectstyle.cayenne.access.DataRowStore.sendUpdateNotification 
(DataRowStore.java:709)  
org.objectstyle.cayenne.access.DataRowStore.processSnapshotChanges 
(DataRowStore.java:574)  
org.objectstyle.cayenne.access.DataDomainFlushAction.postprocess 
(DataDomainFlushAction.java:278)  
org.objectstyle.cayenne.access.DataDomainFlushAction.flush 
(DataDomainFlushAction.java:178)  
org.objectstyle.cayenne.access.DataDomain.onSyncFlush 
(DataDomain.java:846)
org.objectstyle.cayenne.access.DataDomain$2.transform 
(DataDomain.java:817)
org.objectstyle.cayenne.access.DataDomain.runInTransaction 
(DataDomain.java:872)  
org.objectstyle.cayenne.access.DataDomain.onSync(DataDomain.java:814)
org.objectstyle.cayenne.access.DataContext.flushToParent 
(DataContext.java:1262) package test;
public class SerializeDCTest {
    public SerializeDCTest() {
    }
    public static void main(String[] args) {
        //boolean useSharedCache = true; //works
        boolean useSharedCache = false;
        DataContext context = DataContext.createDataContext 
(useSharedCache);
        context = serializeDC(context);
        Employee emp = (Employee) DataObjectUtils.objectForPK 
(context, Employee.class, 740);
        emp.setFirstname("test" + Math.random());
        context.commitChanges();
    }
    public static DataContext serializeDC(DataContext dc) {
        try {
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            oos.writeObject(dc);
            ByteArrayInputStream is = new ByteArrayInputStream 
(bos.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(is);
            DataContext result = (DataContext) ois.readObject();
            return result;
        } catch (Exception ex) {
            throw new RuntimeException("DataContext serialization  
failed", ex);
        }
    }
}
kind regards
bob