Create Data Consistency in Your Entity Bean by Using Persistence

There are two methods for managing the persistent data within an entity bean: bean-managed (BMP) and container-managed persistence (CMP). The main difference between BMP and CMP beans is defined by who manages the persistence of the entity bean's data. With CMP beans, the container manages the persistence—the bean deployment descriptor specifies how to map the data and where the data is stored. With BMP beans, the logic for saving the data and where it is saved is programmed within designated methods. These methods are invoked by the container at the appropriate moments.

In practical terms, the following table provides a definition for both types, and a summary of the programmatic and declarative differences between them:

Management Issues	Bean-Managed Persistence	Container-Managed Persistence
Persistence management	You are required to implement the persistence management within the ejbStore, ejbLoad, ejbCreate, and ejbRemove EntityBean methods. These methods must contain logic for saving and restoring the persistent data. For example, the ejbStore method must have logic in it to store the entity bean's data to the appropriate database. If it does not, the data can be lost.	The management of the persistent data is done for you. That is, the container invokes a persistence manager on behalf of your bean. You use ejbStore and ejbLoad for preparing the data before the commit or for manipulating the data after it is refreshed from the database. The container always invokes the ejbStore method right before the commit. In addition, it always invokes the ejbLoad method right after reinstating CMP data from the database.
Finder methods allowed	The findByPrimaryKey method and other finder methods are allowed.	The findByPrimaryKey method and other finder methods clause are allowed.
Defining CMP fields	N/A	Required within the EJB deployment descriptor. The primary key must also be declared as a CMP field.
Mapping CMP fields to resource destination	N/A	Required. Dependent on persistence manager.
Definition of persistence manager	N/A	Required within the Oracle-specific deployment descriptor. See the next section for a description of a persistence manager.

For more information on container-managed persistence, see Chapter 5, "CMP Entity Beans"; for information on bean-managed persistence, see Chapter 8, "BMP Entity Beans".