(EJB) Entity Beans in brief

What is an Entity Bean?

An Entity bean represents a business object in a persistent storage mechanism. An entity bean typically represents a table in a relational database and each instance represents a row in the table. Entity bean differs from session bean by persistence, shared access, relationship and primary key. There are two types of entity beans available.

• Container Managed Persistence (CMP)
• Bean Managed Persistence (BMP)

CMP / Container Managed Persistence

A The term container-managed persistence means that the EJB container handles all database access required by the entity bean. The bean's code contains no database access (SQL) calls. As a result, the bean's code is not tied to a specific persistent storage mechanism (database). Because of this flexibility, even if you redeploy the same entity bean on different J2EE servers that use different databases, you won't need to modify or recompile the bean's code. So, your entity beans are more portable.

BMP / Bean Managed Persistence

A Bean managed persistence (BMP) occurs when the bean manages its persistence. Here the bean will handle all the database access. So the bean's code contains the necessary SQLs calls. So it is not much portable compared to CMP. Because when we are changing the database we need to rewrite the SQL for supporting the new database.