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/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
* See the lgpl.txt file in the root directory or .
*/
package org.hibernate.annotations;
import org.hibernate.Incubating;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* Maps an entity to a database view. The name of the view is
* determined according to the usual rules regarding table
* mappings, and may be customized using the JPA-standard
* {@link jakarta.persistence.Table @Table} annotation. This
* annotation specifies the query which defines the view,
* allowing the view to be exported by the schema management
* tooling.
*
* For example, this mapping:
*
* @Immutable @Entity
* @Table(name="summary")
* @View(query="select type, sum(amount) as total, avg(amount) as average from details group by type")
* @Synchronize("details")
* public class Summary {
* @Id String type;
* Double total;
* Double average;
* }
*
*
* results in the following generated DDL:
*
* create view summary
* as select type, sum(amount) as total, avg(amount) as average from details group by type
*
*
* If a view is not updatable, we recommend annotating the
* entity {@link Immutable @Immutable}.
*
* It's possible to have an entity class which maps a table,
* and another entity which maps a view defined as a query
* against that table. In this case, a stateful session is
* vulnerable to data aliasing effects, and it is the
* responsibility of client code to ensure that changes to
* the first entity are flushed to the database before
* reading the same data via the second entity. The
* {@link Synchronize @Synchronize} annotation can help
* alleviate this problem, but it's an incomplete solution.
*
* Therefore, we recommend the use of {@linkplain
* org.hibernate.StatelessSession stateless sessions}
* when interacting with entities mapped to views.
*
* @since 6.3
*
* @author Gavin King
*/
@Incubating
@Target(TYPE)
@Retention(RUNTIME)
public @interface View {
/**
* The SQL query that defines the view.
*/
String query();
}