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How can solve the UniqueFieldConstraintViolationException db4o


How can solve the UniqueFieldConstraintViolationException db4o

By : John
Date : November 19 2020, 03:59 PM
will be helpful for those in need The code run ok, but give me a Exception that I can't controlle, This is the console message: , I find the solution to catch the exception:
code :
catch (UniqueFieldValueConstraintViolationException e) {
        System.out.println("The person with this DNI es already exists");
bbdd.rollback();
}


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How should I use DB4O in ASP.NET

How should I use DB4O in ASP.NET


By : Thijs Wouters
Date : March 29 2020, 07:55 AM
I hope this helps you . Check out this forum post from the db4o website, it shows a few good alternatives. In the past I have used a custom HttpModule similar to the one ~7 posts down and it worked well for me.
db4o - DatabaseClosedException

db4o - DatabaseClosedException


By : user3209590
Date : March 29 2020, 07:55 AM
Hope this helps I figured it out ... I didn't have the right scope specified on my bean ... I wrote a simple test application without Weld / CDI and it worked fine. The ObjectServer was getting closed almost immediately after it was opened.
After I changed it to the proper scope which was a singleton for the server, it worked.
db4o - how do I get a distinct list of classes contained in a .db4o DB file?

db4o - how do I get a distinct list of classes contained in a .db4o DB file?


By : Vladimir Dubovets
Date : March 29 2020, 07:55 AM
Hope this helps You can use something like (C# but it can be easily converted to Java :)
code :
const string DatabaseFileName = "c:\\temp\\Learning.odb";
static void Main(string[] args)
{
    using (var db = Db4oEmbedded.OpenFile(DatabaseFileName))
    {
        var classes = db.Ext().StoredClasses();
        foreach (var @class in classes)
        {
            Console.WriteLine();
            Console.WriteLine(@class.GetName());
            foreach (var field in @class.GetStoredFields())
            {
                Console.WriteLine("\t{1} {0}", field.GetName(), field.GetStoredType().GetName());
            }
        }
    }
}
db4o to db4o replication not quite replicating

db4o to db4o replication not quite replicating


By : emdoxn
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I managed to get the version 8 to replicate correctly. I was not following the tutorial exactly and made assumptions (Although without clarification it is still an assumption).
It seems that instantiating the ReplicationSession and the ReplicationProviders at the time of syncing is critical. I changed my code so that at SyncDatabases() these are created and not kept (And I guess garbage collection takes care of them).
code :
public void syncDatabases()
{        
    // First get the changes of the two replication-partners
    Db4oEmbeddedReplicationProvider providerA = new Db4oEmbeddedReplicationProvider(hostContainer);
    Db4oEmbeddedReplicationProvider providerB = new Db4oEmbeddedReplicationProvider(clientContainer);
    ReplicationSession replication = Replication.begin(providerA, providerB);

    ObjectSet<Object> changesOnHost = replication.providerA().objectsChangedSinceLastReplication();
    ObjectSet<Object> changesOnClient = replication.providerB().objectsChangedSinceLastReplication();

    // then iterate over both change-sets and replicate it
    for (Object changedObjectOnClient : changesOnClient)
    {
        replication.replicate(changedObjectOnClient);
    }
    for (Object changedObjectOnHost : changesOnHost)
    {
        replication.replicate(changedObjectOnHost);
    }
    replication.commit();

    replication.replicateDeletions(Object.class);
}
db4o concerns

db4o concerns


By : user3750664
Date : March 29 2020, 07:55 AM
this will help You have to be very careful, because two things can happen: you can pull whole db into memory, or just partial graph (rest of objects will be null).
In db4o there's notion of Activator and Update depth, which can be configured upon dbv40 configuration, or when objects are fetched. Its the way you tell db40 how deep you want him to go when fetching referenced objects. Check db4o web site, there's documentation about it:
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