Question

I am using db4o 8.0.

I have a class

PostedMessage{
    @Indexed
    long receivedTime;
    @Indexed
    long sentTime;
    ...    
    //getter methods and setter methods for all the fields.
}

I persist the PostedMessage objects to db4o database. I have already saved 15000+ objects to db4o database. And now when I run following query, it results in OutOfMemoryError.

    //Query to get PostedMessages between "start" and "end" dates.
    Query q = db.query();
    q.constrain(PostedMessage.class);
    Constraint from = q.descend("receivedTime").constrain(new Long(start.getTimeInMillis())).greater().equal();
    q.descend("receivedTime").constrain(new Long(end.getTimeInMillis())).smaller().equal().and(from);
    q.execute();//results in OutOfMemoryError

To avoid the OutOfMemoryError, I need to add indexes to the fields of PostedMessage class. Read This.

I have a server/client configuration. I don’t have control over pre-configuring the ObjectContainer before opening it.

I will have to apply/append the indexing CommonConfiguration after the ObjectContainer is just opened and provided to me.

I know how to create the config.

    EmbeddedConfiguration appendConfig = Db4oEmbedded.newConfiguration();
    appendConfig.common().objectClass(EmailMessage.class).objectField("receivedTime").indexed(true);
    appendConfig.common().objectClass(EmailMessage.class).objectField("sentTime").indexed(true);

I am not able to figure out how to apply this config to already opened ObjectContainer.
How can I add indexes to the just opened ObjectContainer?

Is EmbeddedConfigurationItem’s apply() method the answer? If it is, can I get a sample code that shows how to use it?

Edited : Added @Indexed annotation later to the question.

Answer 1

cl-r’s suggestion of using TA/TP worked like a charm in my case. See his comment above.

You have also to install Transparent Activation/Transparent
Persistence to avoid to load unnecessary object in memmory. Look at
chapter 10&11 in tutorial (in the doc/tutorial directory of the
downloaded db4o[Version].zip] – cl-r