HHH-10971 - Document flush operation order
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@ -234,4 +234,50 @@ The `INSERT` statement was not executed because the persistence context because
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[NOTE]
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[NOTE]
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====
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This mode is useful when using multi-request logical transactions and only the last request should flush the persistence context.
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This mode is useful when using multi-request logical transactions and only the last request should flush the persistence context.
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====
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[[flushing-order]]
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=== Flush operation order
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From a database perspective, a row state can be altered using either an `INSERT`, an `UPDATE` or a `DELETE` statement.
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Because https://vladmihalcea.com/2014/07/30/a-beginners-guide-to-jpahibernate-entity-state-transitions/[entity state changes] are automatically converted to SQL statements, it's important to know which entity actions are associated to a given SQL statement.
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`INSERT`:: The `INSERT` statement is generated either by the `EntityInsertAction` or `EntityIdentityInsertAction`. These actions are scheduled by the `persist` operation, either explicitly or through cascading the `PersistEvent` from a parent to a child entity.
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`DELETE`:: The `DELETE` statement is generated by the `EntityDeleteAction` or `OrphanRemovalAction`.
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`UPDATE`:: The `UPDATE` statement is generated by `EntityUpdateAction` during flushing if the managed entity has been marked modified. The https://vladmihalcea.com/2014/08/21/the-anatomy-of-hibernate-dirty-checking/[dirty checking mechanism] is responsible for determining if a managed entity has been modified since it was first loaded.
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Hibernate does not execute the SQL statements in the order of their associated entity state operations.
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To visualize how this works, consider the following example:
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[[flushing-order-example]]
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.Flush operation order
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====
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[source, JAVA, indent=0]
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----
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include::{sourcedir}/FlushOrderTest.java[tags=flushing-order-example]
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----
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[source, SQL, indent=0]
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----
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include::{extrasdir}/flushing-order-example.sql[]
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----
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====
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Even if we removed the first entity and then persist a new one, Hibernate is going to execute the `DELETE` statement after the `INSERT`.
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[TIP]
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====
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The order in which SQL statements are executed is given by the `ActionQueue` and not by the order in which entity state operations have been previously defined.
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====
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The `ActionQueue` executes all operations in the following order:
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. `OrphanRemovalAction`
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. `EntityInsertAction` or `EntityIdentityInsertAction`
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. `EntityUpdateAction`
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. `CollectionRemoveAction`
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. `CollectionUpdateAction`
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. `CollectionRecreateAction`
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. `EntityDeleteAction`
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@ -0,0 +1,5 @@
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INSERT INTO Person (name, id)
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VALUES ('John Doe', 2L)
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DELETE FROM Person WHERE id = 1
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@ -0,0 +1,89 @@
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/*
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* Hibernate, Relational Persistence for Idiomatic Java
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*
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* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
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* See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
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*/
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package org.hibernate.userguide.flush;
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import javax.persistence.Entity;
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import javax.persistence.Id;
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import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
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import org.junit.Test;
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import org.jboss.logging.Logger;
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import static org.hibernate.testing.transaction.TransactionUtil.doInJPA;
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/**
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* @author Vlad Mihalcea
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*/
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public class FlushOrderTest extends BaseEntityManagerFunctionalTestCase {
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private static final Logger log = Logger.getLogger( FlushOrderTest.class);
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@Override
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protected Class<?>[] getAnnotatedClasses() {
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return new Class<?>[]{
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Person.class
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};
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}
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@Test
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public void testOrder() {
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doInJPA( this::entityManagerFactory, entityManager -> {
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entityManager.createNativeQuery("delete from Person").executeUpdate();
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});
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doInJPA( this::entityManagerFactory, entityManager -> {
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Person person = new Person("John Doe");
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person.id = 1L;
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entityManager.persist(person);
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});
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doInJPA( this::entityManagerFactory, entityManager -> {
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log.info("testFlushSQL");
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//tag::flushing-order-example[]
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Person person = entityManager.find( Person.class, 1L);
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entityManager.remove(person);
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Person newPerson = new Person( );
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newPerson.setId( 2L );
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newPerson.setName( "John Doe" );
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entityManager.persist( newPerson );
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//end::flushing-order-example[]
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});
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}
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@Entity(name = "Person")
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public static class Person {
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@Id
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private Long id;
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private String name;
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public Person() {
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}
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public Person(String name) {
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this.name = name;
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}
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public Long getId() {
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return id;
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}
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public void setId(Long id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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}
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}
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