It could be because OpenJPA does not know about your foreign keys... You have to tell OpenJPA that there is a foreign key using the @ForeignKey annotation or instruct OpenJPA to detect the foreign keys by inspecting your schema. To do this, you have to specify the following property in your persistence.xml:
<property name="openjpa.jdbc.SchemaFactory" value="native(ForeignKeys=true)" /> Hope this helps! Christian
