Entity beans must employ CMTs, and so they contain no transaction demarcation code.
Entity beans may delegate their persistence to the container. This is known as container-managed persistence (CMP). In such cases the bean no longer contains code to synchronize its attributes with the data store.
JDO as the underlying technology for CMP implementations
Incidentally, an EJB container may utilize JDO internally in support of its CMP implementation. However, that is of architectural significance only and makes no difference to the bean implementation.
The rest of this discussion centers on bean-managed persistence. To implement a BMP entity bean with JDO, the bean should hold a reference to one (or more) ...