Access intent policies
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. You can set access intents only within EJB V2.x-compliant modules for entity beans with CMP V2.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 method-based policy is acted upon by the combination of the EJB container and persistence manager when the method causes the entity to load.
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.
Concurrency control
Read-ahead hints
Using access intent policies
Access intent -- isolation levels and update locks
Access intent exceptions