An access intent policy is a named set of properties (access intents) that governs data access for Enterprise JavaBeans (EJB) persistence. You can assign policies to an entity bean and to individual methods on an entity bean's home, remote, or local interfaces during assembly. If you have WebSphere Application Server Enterprise Edition version 5.0.x, or WebSphere Business Integration Server Foundation version 5.1 or later installed, you can assign these during development as well. You can set access intents only within EJB Version 2.x-compliant modules for entity beans with bean-managed persistence or with CMP Version 2.x.
This product supplies a number of access intent policies that specify permutations of read intent and concurrency control; the pessimistic/update policy can be qualified further. The selected policy determines the appropriate isolation level and locking strategy used by the run time environment.
Access intent policies are specifically designed to supplant the use of isolation level and access intent method-level modifiers found in the extended deployment descriptor for EJB version 1.1 enterprise beans. You cannot specify isolation level and read-only modifiers for EJB version 2.0 enterprise beans.
Access intent policies configured on an entity basis
define the default access intent for that entity. The default access intent
controls the entity unless you specify a different access intent policy based
on either method-level configuration or application profiling
You can use application profiling or method level
access intent policies to control access intent more precisely. Application
profiling is only available in the WebSphere Application Server Enterprise
edition version 5.0.x and WebSphere Business Integration Server Foundation
version 5.1.x products. Method-level access intent policies are
named and defined at the module level. A module can have one or many such
policies. Policies are assigned, and apply, to individual methods of the declared
interfaces of entity beans and their associated home interfaces. A policy is acted upon by either the combination of
the EJB container and persistence manager (for entity beans with container-managed
persistence) or directly by entity beans with bean-managed persistence.
For entity beans that are backed by tables with nullable columns, use an optimistic policy with caution. Nullable columns are automatically excluded from overqualified updates at deployment time; concurrent changes to a nullable field might result in lost updates. When used with the IBM WebSphere Studio Application Developer product, this product provides support for selecting a subset of the non-nullable columns that are to be reflected in the overqualified update statement that is generated in the deployment code to support optimistic policies.
An entity that is configured with a read-only policy
that causes a bean to be activated can cause problems if updates are attempted
within the same transaction. Those changes are not committed, and the process
throws an exception because data integrity might be compromised.