How to solve "Temporary ID hasn't been replaced on commit" with Cayenne

When committing changes to a Apache Cayenne context, I get an exception like the following.

org.apache.cayenne.CayenneRuntimeException: [v.3.0.1 Sep 06 2010 15:09:38]
Temporary ID hasn't been replaced on commit

Why does this exception occur?

You are trying to commit an object for which Cayenne does not know how to generate a permanent id. This in turn typically happens when the underlying table has no primary key defined.

To solve the problem, do one of the following.

• Add a primary key to the underlying table, either a surrogate key (new generated id column) or a natural key (combination of existing columns).
• Set your own permanent id on the object(s) in question using the PersistentObject.setObjectID() method.