An access intent policy is a named set of properties (access intents) that governs data access for Enterprise JavaBeans (EJB) persistence. You can assign a policy to individual methods on an entity bean's home, remote, or local interfaces during assembly. Access intents are settable only within EJB Version 2.x-compliant modules for entity beans 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 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 the combination of the EJB container and persistence manager.
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 nonnullable columns that are to be reflected in the overqualified update statement that is generated in the deployment code to support optimistic policies.
A method 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 will not be committed, and an exception will be thrown because data integrity might be compromised.