Correct document about spring.jpa.generate-ddl and add tests

Closes spring-projectsGH-40177

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.orm.jpa;
 
+import java.io.File;
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
@@ -40,6 +41,7 @@
 import org.hibernate.boot.model.naming.CamelCaseToUnderscoresNamingStrategy;
 import org.hibernate.boot.model.naming.ImplicitNamingStrategy;
 import org.hibernate.boot.model.naming.PhysicalNamingStrategy;
+import org.hibernate.cfg.AvailableSettings;
 import org.hibernate.cfg.ManagedBeanSettings;
 import org.hibernate.cfg.SchemaToolingSettings;
 import org.hibernate.dialect.H2Dialect;
@@ -76,6 +78,7 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.event.ContextRefreshedEvent;
+import org.springframework.orm.jpa.AbstractEntityManagerFactoryBean;
 import org.springframework.orm.jpa.JpaTransactionManager;
 import org.springframework.orm.jpa.JpaVendorAdapter;
 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
@@ -98,6 +101,7 @@
  * @author Stephane Nicoll
  * @author Chris Bono
  * @author Moritz Halbritter
+ * @author Yanming Zhou
  */
 class HibernateJpaAutoConfigurationTests extends AbstractJpaAutoConfigurationTests {
 
@@ -182,6 +186,50 @@ void hibernateDialectIsSetWhenDatabasePlatformIsSet() {
 				.contains(entry("hibernate.dialect", databasePlatform))));
 	}
 
+	@Test
+	void jpaGenerateDdlIsUsedIfHibernateHbm2ddlAutoIsNotSet() {
+		try {
+			contextRunner().withPropertyValues("spring.jpa.generate-ddl=true", "spring.datasource.url=jdbc:h2:./test")
+				// simulate non-embedded database
+				// see HibernateDefaultDdlAutoProvider.getDefaultDdlAuto(DataSource)
+				.run(assertEntityManagerFactoryBean((adapter) -> assertThat(adapter.getJpaPropertyMap())
+					.containsEntry(AvailableSettings.HBM2DDL_AUTO, "update")));
+		}
+		finally {
+			// cleanup H2 database file
+			File db = new File("test.mv.db");
+			if (db.exists()) {
+				db.delete();
+			}
+		}
+	}
+
+	@Test
+	void jpaGenerateDdlIsNotUsedIfHibernateHbm2ddlAutoIsSetToNone() {
+		contextRunner()
+			.withPropertyValues("spring.jpa.generate-ddl=true", "spring.jpa.properties.hibernate.hbm2ddl.auto=none")
+			.run(assertEntityManagerFactoryBean((adapter) -> assertThat(adapter.getJpaPropertyMap())
+				.containsEntry(AvailableSettings.HBM2DDL_AUTO, "none")));
+	}
+
+	@Test
+	void jpaGenerateDdlIsNotUsedIfHibernateHbm2ddlAutoIsSetToOtherThanNone() {
+		contextRunner()
+			.withPropertyValues("spring.jpa.generate-ddl=true", "spring.jpa.properties.hibernate.hbm2ddl.auto=create")
+			.run(assertEntityManagerFactoryBean((adapter) -> assertThat(adapter.getJpaPropertyMap())
+				.containsEntry(AvailableSettings.HBM2DDL_AUTO, "create")));
+	}
+
+	private ContextConsumer<AssertableApplicationContext> assertEntityManagerFactoryBean(
+			Consumer<AbstractEntityManagerFactoryBean> adapter) {
+		return (context) -> {
+			assertThat(context).hasSingleBean(JpaVendorAdapter.class);
+			assertThat(context).hasSingleBean(HibernateJpaVendorAdapter.class);
+			assertThat(context).hasSingleBean(AbstractEntityManagerFactoryBean.class);
+			adapter.accept(context.getBean(AbstractEntityManagerFactoryBean.class));
+		};
+	}
+
 	private ContextConsumer<AssertableApplicationContext> assertJpaVendorAdapter(
 			Consumer<HibernateJpaVendorAdapter> adapter) {
 		return (context) -> {

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/data/sql.adoc

@@ -307,7 +307,7 @@ spring:
 The line in the preceding example passes a value of `true` for the `hibernate.globally_quoted_identifiers` property to the Hibernate entity manager.
 
 By default, the DDL execution (or validation) is deferred until the `ApplicationContext` has started.
-There is also a `spring.jpa.generate-ddl` flag, but it is not used if Hibernate auto-configuration is active, because the `ddl-auto` settings are more fine-grained.
+There is also a `spring.jpa.generate-ddl` flag, but it is not used if `spring.jpa.hibernate.ddl-auto` or `spring.jpa.properties.hibernate.hbm2ddl.auto` is present, because they are more fine-grained.