Revision as of 15:53, 12 January 2011

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JPQL

You may define queries in metadata annotations or the XML descriptor.

You can use update and delete queries to persist your changes with JP QL.

You can perform bulk update of entities with the UPDATE statement. This statement operates on a single entity type and sets one or more single-valued properties of the entity subject to the condition in the WHERE clause. Update queries provide an equivalent to the SQL UPDATE statement, but with JP QL conditional expressions.

This example demonstrates how to use an update query to give employees a raise. The WHERE clause contains the conditional expression.

Update Query

 UPDATE Employee e
 SET e.salary = 60000
 WHERE e.salary = 50000

You can perform bulk removal of entities with the DELETE statement. Delete queries provide an equivalent to the SQL DELETE statement, but with JP QL conditional expressions.

This example demonstrates how to use a delete query to remove all employees who are not assigned to a department. The WHERE clause contains the conditional expression.

Delete Query

 DELETE FROM Employee e
 WHERE e.department IS NULL

The persistence context is not updated to reflect results of update and delete operations. If you use a transaction-scoped persistence context, you should either execute the bulk operation in a transaction all by itself, or be the first operation in the transaction (see Introduction to EclipseLink Transactions). That is because any entity actively managed by the persistence context will remain unaware of the actual changes occurring at the database level.

For more information, see Chapter 4 "Query Language" in the JPA Specification.

For more information and examples, see the following:

• What You May Need to Know About Querying with Java Persistence Query Language
• Queries
• Named Queries

Overview	Querying	Criteria
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