I came across this question after searching for a ODBC or JDBC. To my surprise, since I am new to db4o I found there are tools to browse db4o, including a Netbeans and Eclipse plug in. However, when it comes to the question at hand, I only found one company, and the product is not being sold nor demoed (makes me think is not ready yet).
So, how do you transfer data? Is there a tool or script I have not found yet?
In my opinion, this comes down to the Object-relational impedance mismatch. Which is to say, except in very simple cases, there isn't necessarily a direct translation from a database row to an object. Your object model is fundamentally different than your database schema. Therefore, I would imagine that in most cases, you will have to come up with the mapping (and a migration application) yourself.
This goes generally for any relational database/object database, not just SQL Server and db4o.
Data transfer between db4o and relational Databases (in both direction) can be easily done with db4o's tool: dRS - db4o Replication System (based on Hibernate). BTW, db4o user forum might be very useful, you will get answers directly from core developers.
That's right. When it comes to db4o's dRS, in order to move your data to a relational database you need to define a Hibernate mapping. But it's definitely the way to go for this kind of migration if you don't want to do it all by yourself.
Best!