Use WSJPA access intent

Use WSJPA access intent

Java Persistence API (JPA) access intent specifies the isolation level and lock level used when reading data from a data source. Access intent controls the Java Database Connectivity (JDBC) isolation level and whether read, update, or exclusive locks are acquired when retrieving data.

For a JPA persistence provider on the application server, the application can specify isolation and ReadLockMode based on a TaskName. The TaskName provides a better control over applying these characteristics. The application defines a set of entity types and corresponding access intent for each TaskName defined in a persistence unit.
JPA access intent is a JPA for the WebSphere (WSJPA) extension of OpenJPA.
Restriction:

Access intent is available for application in the Java EE server environment
Access intent is applicable to non-query entity manager interface methods. Query uses query hint interface to set its isolation and read lock values.
Access intent is only available for DB2 databases.
Access intent is in effect only when pessimistic lock manager is used. Add the following to the persistence unit property list. <property name="openjpa.LockManager" value="pessimistic"/>

WebSphere EJB 2.x entity bean access intent JPA access intent Description
optimistic isolation: Read Committed Data is read but no lock is held. Version ID is used on update to ensure data integrity. Other transactions can read and update data.
lockManager: Optimistic
query Hint: ReadLockMode: READ
pessimistic read isolation: Repeatable Read Data is read with shared locks. Other transactions attempting to update data are blocked.
lockManager: Optimistic
query Hint: ReadLockMode: READ
pessimistic update isolation: Repeatable Read Data is retrieved with update or exclusive lock. Other writes are blocked until commit. This access intent can be used to serialize update access to data when there are multiple writers.
lockManager: Pessimistic
query Hint: ReadLockMode: WRITE
pessimistic exclusive isolation: Serializable Data is retrieved with update or exclusive lock. Other writes are blocked until commit. This access intent can be used to serialize update access to data when there are multiple writers.
lockManager: Pessimistic
query Hint: ReadLockMode:WRITE

A TaskName is set on a transaction context by one of the following:

TaskName is automatically set in the EJB container when a transaction begins using WebSphere local transaction (EJB unspecified transaction), JTA global transaction in a Container-Managed Transaction (CMT) or user-initiated global transaction in a Bean-Managed Transaction (BMT).
TaskName is manually set in an application using the TaskNameAccessor API provided for JPA.

Use task names supports the specification of access intent on a request scope rather than specifying it in the persistence.xml file, which has an application scope across all entities. Often a query is contained in a method or component which is used in many different transaction contexts. Some of these contexts might require repeatable-read and update lock intent but other contexts do not.

Isolation level and read locks can be specified on:

An application scope in the persistence.xml file. These isolation levels and read lock types are properties specified in the persistence.xml file. They apply to all entities defined in the persistence unit.
A transaction scope in the task name. Transaction scoped hints override application scope values.
Query instance with a query hint. Query hint can be used to override isolation and ReadLockMode for a particular query instance. A query hint overrides isolation level and read locks specified at the application or transaction scope.

Tasks

Set a TaskName using TaskNameAccessor API This task explains how to use the TaskNameAccessor API to set JPA TaskName at run time.
Specify TaskName in a JPA persistence unit This task explains how to specify a TaskName in JPA persistence unit .

What to do next
For more information about Access intent, see the topic, Access intent service.

Subtopics

Setting a TaskName using TaskNameAccessor API
Using the TaskNameAccessor API to set Java Persistence API (JPA) TaskName at runtime.
Specify TaskName in a JPA persistence unit
Specifying a TaskName in Java Persistence API (JPA) persistence unit
Setting a TaskName using TaskNameAccessor API
Using the TaskNameAccessor API to set Java Persistence API (JPA) TaskName at runtime.
Specify TaskName in a JPA persistence unit
Specifying a TaskName in Java Persistence API (JPA) persistence unit

Related:

Access intent service
Task overview: Store and retrieve persistent data with the JPA API
Troubleshoot JPA applications

WebSphere EJB 2.x entity bean access intent	JPA access intent	Description
optimistic	isolation: Read Committed	Data is read but no lock is held. Version ID is used on update to ensure data integrity. Other transactions can read and update data.
	lockManager: Optimistic
	query Hint: ReadLockMode: READ
pessimistic read	isolation: Repeatable Read	Data is read with shared locks. Other transactions attempting to update data are blocked.
	lockManager: Optimistic
	query Hint: ReadLockMode: READ
pessimistic update	isolation: Repeatable Read	Data is retrieved with update or exclusive lock. Other writes are blocked until commit. This access intent can be used to serialize update access to data when there are multiple writers.
	lockManager: Pessimistic
	query Hint: ReadLockMode: WRITE
pessimistic exclusive	isolation: Serializable	Data is retrieved with update or exclusive lock. Other writes are blocked until commit. This access intent can be used to serialize update access to data when there are multiple writers.
	lockManager: Pessimistic
	query Hint: ReadLockMode:WRITE