Let Hibernate detect the dialect to use

Closes gh-16172

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/orm/jpa/JpaBaseConfiguration.java

@@ -105,8 +105,12 @@ public abstract class JpaBaseConfiguration implements BeanFactoryAware {
 	public JpaVendorAdapter jpaVendorAdapter() {
 		AbstractJpaVendorAdapter adapter = createJpaVendorAdapter();
 		adapter.setShowSql(this.properties.isShowSql());
-		adapter.setDatabase(this.properties.determineDatabase(this.dataSource));
-		adapter.setDatabasePlatform(this.properties.getDatabasePlatform());
+		if (this.properties.getDatabase() != null) {
+			adapter.setDatabase(this.properties.getDatabase());
+		}
+		if (this.properties.getDatabasePlatform() != null) {
+			adapter.setDatabasePlatform(this.properties.getDatabasePlatform());
+		}
 		adapter.setGenerateDdl(this.properties.isGenerateDdl());
 		return adapter;
 	}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/orm/jpa/JpaProperties.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -134,7 +134,10 @@ public class JpaProperties {
 	 * {@link DataSource}.
 	 * @param dataSource the auto-configured data source
 	 * @return {@code Database}
+	 * @deprecated since 2.2.0 in favor of letting the JPA container detect the database
+	 * to use.
 	 */
+	@Deprecated
 	public Database determineDatabase(DataSource dataSource) {
 		if (this.database != null) {
 			return this.database;

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

@@ -110,14 +110,14 @@ public class CustomHibernateJpaAutoConfigurationTests {
 	}
 
 	@Test
-	public void defaultDatabaseForH2() {
+	public void defaultDatabaseIsSet() {
 		this.contextRunner.withPropertyValues("spring.datasource.url:jdbc:h2:mem:testdb",
 				"spring.datasource.initialization-mode:never").run((context) -> {
 					HibernateJpaVendorAdapter bean = context
 							.getBean(HibernateJpaVendorAdapter.class);
 					Database database = (Database) ReflectionTestUtils.getField(bean,
 							"database");
-					assertThat(database).isEqualTo(Database.H2);
+					assertThat(database).isEqualTo(Database.DEFAULT);
 				});
 	}
 

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

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -44,25 +44,6 @@ public class HibernateDefaultDdlAutoProviderTests {
 					HibernateJpaAutoConfiguration.class))
 			.withPropertyValues("spring.datasource.initialization-mode:never");
 
-	@Test
-	public void defaultDdlAutoForMysql() {
-		// Set up environment so we get a MySQL database but don't require server to be
-		// running...
-		this.contextRunner.withPropertyValues(
-				"spring.datasource.type:"
-						+ org.apache.tomcat.jdbc.pool.DataSource.class.getName(),
-				"spring.datasource.database:mysql",
-				"spring.datasource.url:jdbc:mysql://localhost/nonexistent",
-				"spring.jpa.database:MYSQL").run((context) -> {
-					HibernateDefaultDdlAutoProvider ddlAutoProvider = new HibernateDefaultDdlAutoProvider(
-							Collections.emptyList());
-					assertThat(ddlAutoProvider
-							.getDefaultDdlAuto(context.getBean(DataSource.class)))
-									.isEqualTo("none");
-
-				});
-	}
-
 	@Test
 	public void defaultDDlAutoForEmbedded() {
 		this.contextRunner.run((context) -> {

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

@@ -25,6 +25,7 @@ import java.util.Collections;
 import java.util.Enumeration;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Consumer;
 
 import javax.persistence.EntityManager;
 import javax.persistence.EntityManagerFactory;
@@ -37,6 +38,7 @@ import com.zaxxer.hikari.HikariDataSource;
 import org.hibernate.boot.model.naming.ImplicitNamingStrategy;
 import org.hibernate.boot.model.naming.PhysicalNamingStrategy;
 import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.dialect.H2Dialect;
 import org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform;
 import org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform;
 import org.hibernate.internal.SessionFactoryImpl;
@@ -65,7 +67,9 @@ import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.orm.jpa.JpaTransactionManager;
+import org.springframework.orm.jpa.JpaVendorAdapter;
 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
+import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -155,6 +159,40 @@ public class HibernateJpaAutoConfigurationTests
 				.run((context) -> assertThat(context).hasNotFailed());
 	}
 
+	@Test
+	public void hibernateDialectIsNotSetByDefault() {
+		contextRunner().run(assertJpaVendorAdapter(
+				(adapter) -> assertThat(adapter.getJpaPropertyMap())
+						.doesNotContainKeys("hibernate.dialect")));
+	}
+
+	@Test
+	public void hibernateDialectIsSetWhenDatabaseIsSet() {
+		contextRunner().withPropertyValues("spring.jpa.database=H2")
+				.run(assertJpaVendorAdapter(
+						(adapter) -> assertThat(adapter.getJpaPropertyMap()).contains(
+								entry("hibernate.dialect", H2Dialect.class.getName()))));
+	}
+
+	@Test
+	public void hibernateDialectIsSetWhenDatabasePlatformIsSet() {
+		String databasePlatform = TestH2Dialect.class.getName();
+		contextRunner()
+				.withPropertyValues("spring.jpa.database-platform=" + databasePlatform)
+				.run(assertJpaVendorAdapter(
+						(adapter) -> assertThat(adapter.getJpaPropertyMap())
+								.contains(entry("hibernate.dialect", databasePlatform))));
+	}
+
+	private ContextConsumer<AssertableApplicationContext> assertJpaVendorAdapter(
+			Consumer<HibernateJpaVendorAdapter> adapter) {
+		return (context) -> {
+			assertThat(context).hasSingleBean(JpaVendorAdapter.class);
+			assertThat(context).hasSingleBean(HibernateJpaVendorAdapter.class);
+			adapter.accept(context.getBean(HibernateJpaVendorAdapter.class));
+		};
+	}
+
 	@Test
 	public void jtaDefaultPlatform() {
 		contextRunner()
@@ -597,4 +635,8 @@ public class HibernateJpaAutoConfigurationTests
 
 	}
 
+	public static class TestH2Dialect extends H2Dialect {
+
+	}
+
 }

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -1926,15 +1926,8 @@ conditions, it has different defaults. If an embedded database is used and no sc
 manager (such as Liquibase or Flyway) is handling the `DataSource`, it defaults to
 `create-drop`. In all other cases, it defaults to `none`.
 
-The dialect to use is also automatically detected based on the current `DataSource`, but
-you can set `spring.jpa.database` yourself if you want to be explicit and bypass that
-check on startup.
-
-NOTE: Specifying a `database` leads to the configuration of a well-defined Hibernate
-dialect. Several databases have more than one `Dialect`, and this may not suit your needs.
-In that case, you can either set `spring.jpa.database` to `default` to let Hibernate
-figure things out or set the dialect by setting the `spring.jpa.database-platform`
-property.
+The dialect to use is detected by the JPA provider. If you prefer to set the dialect
+yourself, set the `spring.jpa.database-platform` property.
 
 The most common options to set are shown in the following example: