Is there a configuration parameter to set this?
You can set cascade delete using annotations (see also the Orphan Removal section).
JDO defines similar annotations, and both JPA and JDO support this setting also in XML files, but no additional parameters exist in ObjectDB configuration.
You cannot set global cascade delete since that will be too risky - you may delete the entire database.
ObjectDB - Fast Object Database for Java (JPA/JDO)