Hello, thank you for your reply, sorry if I did not make myself clear in the first place. In the above example, the "@OneToMany" annotation represents the mapping of a Java Map object. The "Hibernate Reference Documentation 3.6.10.Final" indeed states in chapter "7.2.2.2. Maps" that it is the correct way to "map a Map" (so to speak).

From the database point of view, the Map is represented by an association table (named "customer_order" in the above example), which has 3 columns:

• one column referencing the Map's owner ("customer_id" above)
• one column holding the Map's key ("somekey" above)
• one column referencing the Map's value ("order_id" above)

So far so good. My point is, a seemingly improper "unique" database constraint is automatically generated on the "order_id" column of the "customer_order" relation table (when Hibernate is configured to generate the DDL automatically). This prevents different Customers to map the same Order object (not really useful in the real customer-order life, but you see the technical point). May be I interpret wrongly the true meaning of "@OneToMany", which inconditionally imposes distinct Orders, whatever the underlying collection nature (Map in my case). May be I should have used the newer annotation "@CollectionOfElements" instead of "@OneToMany" (unfortunately I do not have my testing environment at disposal for the moment), and in this case the bug is only related to the Hibernate Reference Documentation.

What I notice, though, when the Map value is a "primitive" object (such as a String) instead of an "Order", the "unique" DDL constraint is not generated. The DDL generation behaviour thus does not seem consistent at least.