HHH-10826 Auxiliary Database Object no longer documented

HHH-10334 @formula annotation javadoc contains database dependent sample usage

Created a new section related to automatic schema generation

documentation/src/main/asciidoc/userguide/Hibernate_User_Guide.adoc

@@ -10,6 +10,7 @@ include::Preface.adoc[]
 include::chapters/architecture/Architecture.adoc[]
 include::chapters/domain/DomainModel.adoc[]
 include::chapters/bootstrap/Bootstrap.adoc[]
+include::chapters/schema/Schema.adoc[]
 include::chapters/pc/PersistenceContext.adoc[]
 include::chapters/flushing/Flushing.adoc[]
 include::chapters/jdbc/Database_Access.adoc[]

documentation/src/main/asciidoc/userguide/appendices/Configurations.adoc

@@ -556,7 +556,7 @@ Hibernate historically also accepted `hibernate.hbm2ddl.import_files` for a simi
 Comma-separated names of the optional files containing SQL DML statements executed during the `SessionFactory` creation.
 File order matters, the statements of a give file are executed before the statements of the following one.
 
-These statements are only executed if the schema is created, meaning that `hibernate.hbm2ddl.auto` is set to `create` or `create-drop`.
+These statements are only executed if the schema is created, meaning that `hibernate.hbm2ddl.auto` is set to `create`, `create-drop`, or `update`.
 `javax.persistence.schema-generation.create-script-source` / `javax.persistence.schema-generation.drop-script-source` should be preferred.
 
 |`javax.persistence.sql-load-script-source` | |

documentation/src/main/asciidoc/userguide/chapters/domain/basic_types.adoc

@@ -1172,6 +1172,11 @@ include::{extrasdir}/basic/mapping-column-read-and-write-composite-type-persiste
 Sometimes, you want the Database to do some computation for you rather than in the JVM, you might also create some kind of virtual column.
 You can use a SQL fragment (aka formula) instead of mapping a property into a column. This kind of property is read only (its value is calculated by your formula fragment)
 
+[NOTE]
+====
+You should be aware that the `@Formula` annotation takes a native SQL clause which can affect database portability.
+====
+
 [[mapping-column-formula-example]]
 .`@Formula` mapping usage
 ====

documentation/src/main/asciidoc/userguide/chapters/schema/Schema.adoc

@@ -0,0 +1,87 @@
+[[schema-generation]]
+== Schema generation
+:sourcedir: ../../../../../test/java/org/hibernate/userguide/schema
+:extrasdir: extras
+:resourcesdir: ../../../../../test/resources
+
+
+Hibernate allows you to generate the database from the entity mappings.
+
+[TIP]
+====
+Although the automatic schema generation is very useful for testing and prototyping purposes, in a production environment,
+it's much more flexible to manage the schema using incremental migration scripts.
+====
+
+Traditionally, the process of generating  schema from entity mapping has been called `HBM2DDL`.
+To get a list of Hibernate-native and JPA-specific configuration properties consider reading the <<appendices/Configurations.adoc#configurations-hbmddl,Configurations>> section.
+
+Considering the following Domain Model:
+
+[[schema-generation-domain-model-example]]
+.Schema generation Domain Model
+====
+[source, JAVA, indent=0]
+----
+include::{sourcedir}/SchemaGenerationTest.java[tags=schema-generation-domain-model-example]
+----
+====
+
+If the `hibernate.hbm2ddl.auto` configuration is set to `create`, Hibernate is going to generate the following database schema:
+
+[[sql-schema-generation-domain-model-example]]
+.Auto-generated database schema
+====
+[source, SQL, indent=0]
+----
+include::{extrasdir}/sql-schema-generation-domain-model-example.sql[]
+----
+====
+
+=== Importing script files
+
+To customize the schema generation process, the `hibernate.hbm2ddl.import_files` configuration property must be used to provide other scripts files that Hibernate can use when the `SessionFactory` is started.
+
+For instance, considering the following `schema-generation.sql` import file:
+
+[[schema-generation-import-file-example]]
+.Schema generation import file
+====
+[source, JAVA, indent=0]
+----
+include::{resourcesdir}/schema-generation.sql[]
+----
+====
+
+If we configure Hibernate to import the script above:
+
+[[schema-generation-import-file-configuration-example]]
+.Enabling query cache
+====
+[source, XML, indent=0]
+----
+<property
+    name="hibernate.hbm2ddl.import_files"
+    value="schema-generation.sql" />
+----
+====
+
+Hibernate is going to execute the script file after the schema is automatically generated.
+
+=== Database objects
+
+Hibernate allows you to customize the schema generation process via the HBM `database-object` element.
+
+Considering the following HBM mapping:
+
+[[schema-generation-database-object-example]]
+.Schema generation HBM database-object
+====
+[source, JAVA, indent=0]
+----
+include::{sourcedir}/SchemaGenerationTest.hbm.xml[]
+----
+====
+
+When the `SessionFactory` is bootstrapped, Hibernate is going to execute the `database-object`, therefore creating the `sp_count_books` funtion.
+

documentation/src/main/asciidoc/userguide/chapters/schema/extras/sql-schema-generation-domain-model-example.sql

@@ -0,0 +1,29 @@
+create table Customer (
+    id integer not null,
+    accountsPayableXrefId binary,
+    image blob,
+    name varchar(255),
+    primary key (id)
+)
+
+create table Book (
+    id bigint not null,
+    isbn varchar(255),
+    title varchar(255),
+    author_id bigint,
+    primary key (id)
+)
+
+create table Person (
+    id bigint not null,
+    name varchar(255),
+    primary key (id)
+)
+
+alter table Book
+    add constraint UK_u31e1frmjp9mxf8k8tmp990i unique (isbn)
+
+alter table Book
+    add constraint FKrxrgiajod1le3gii8whx2doie
+    foreign key (author_id)
+    references Person

documentation/src/test/java/org/hibernate/userguide/schema/SchemaGenerationTest.hbm.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0"?>
+<!DOCTYPE hibernate-mapping PUBLIC
+        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
+        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd" >
+
+<hibernate-mapping>
+    <database-object>
+        <create>
+            CREATE OR REPLACE FUNCTION sp_count_books(
+                IN authorId bigint,
+                OUT bookCount bigint)
+                RETURNS bigint AS
+            $BODY$
+                BEGIN
+                    SELECT COUNT(*) INTO bookCount
+                    FROM book
+                    WHERE author_id = authorId;
+                END;
+            $BODY$
+            LANGUAGE plpgsql;
+        </create>
+        <drop></drop>
+        <dialect-scope name="org.hibernate.dialect.PostgreSQL95Dialect" />
+    </database-object>
+</hibernate-mapping>

documentation/src/test/java/org/hibernate/userguide/schema/SchemaGenerationTest.java

@@ -0,0 +1,204 @@
+/*
+ * 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 <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.userguide.schema;
+
+import java.sql.Blob;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+import javax.persistence.Basic;
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.Id;
+import javax.persistence.Lob;
+import javax.persistence.ManyToOne;
+import javax.persistence.OneToMany;
+
+import org.hibernate.annotations.LazyGroup;
+import org.hibernate.annotations.NaturalId;
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.dialect.H2Dialect;
+import org.hibernate.dialect.PostgreSQL81Dialect;
+import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
+
+import org.hibernate.testing.RequiresDialect;
+import org.junit.Test;
+
+/**
+ * @author Vlad Mihalcea
+ */
+public class SchemaGenerationTest extends BaseEntityManagerFunctionalTestCase {
+
+	@Override
+	protected Class<?>[] getAnnotatedClasses() {
+		return new Class<?>[] {
+			Person.class,
+			Book.class,
+			Customer.class
+		};
+	}
+
+	@Override
+	protected void addConfigOptions(Map options) {
+		if ( getDialect().getClass().equals( H2Dialect.class ) ) {
+			options.put(
+					AvailableSettings.HBM2DDL_IMPORT_FILES,
+					"schema-generation.sql"
+			);
+			options.put( org.hibernate.cfg.AvailableSettings.HBM2DDL_AUTO, "update" );
+		}
+	}
+
+	@Override
+	protected String[] getMappings() {
+		if ( PostgreSQL81Dialect.class.isAssignableFrom( getDialect().getClass() ) ) {
+			return new String[] { "org/hibernate/userguide/schema/SchemaGenerationTest.hbm.xml" };
+		}
+		return super.getMappings();
+	}
+
+	@Test
+	@RequiresDialect( H2Dialect.class )
+	public void testH2() {
+	}
+
+	@Test
+	@RequiresDialect( PostgreSQL81Dialect.class )
+	public void testPostgres() {
+	}
+
+	//tag::schema-generation-domain-model-example[]
+	@Entity(name = "Customer")
+	public class Customer {
+
+		@Id
+		private Integer id;
+
+		private String name;
+
+		@Basic( fetch = FetchType.LAZY )
+		private UUID accountsPayableXrefId;
+
+		@Lob
+		@Basic( fetch = FetchType.LAZY )
+		@LazyGroup( "lobs" )
+		private Blob image;
+
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public UUID getAccountsPayableXrefId() {
+			return accountsPayableXrefId;
+		}
+
+		public void setAccountsPayableXrefId(UUID accountsPayableXrefId) {
+			this.accountsPayableXrefId = accountsPayableXrefId;
+		}
+
+		public Blob getImage() {
+			return image;
+		}
+
+		public void setImage(Blob image) {
+			this.image = image;
+		}
+	}
+
+	@Entity(name = "Person")
+	public static class Person {
+
+		@Id
+		private Long id;
+
+		private String name;
+
+		@OneToMany(mappedBy = "author")
+		private List<Book> books = new ArrayList<>(  );
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public List<Book> getBooks() {
+			return books;
+		}
+	}
+
+	@Entity(name = "Book")
+	public static class Book {
+
+		@Id
+		private Long id;
+
+		private String title;
+
+		@NaturalId
+		private String isbn;
+
+		@ManyToOne
+		private Person author;
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getTitle() {
+			return title;
+		}
+
+		public void setTitle(String title) {
+			this.title = title;
+		}
+
+		public Person getAuthor() {
+			return author;
+		}
+
+		public void setAuthor(Person author) {
+			this.author = author;
+		}
+
+		public String getIsbn() {
+			return isbn;
+		}
+
+		public void setIsbn(String isbn) {
+			this.isbn = isbn;
+		}
+	}
+	//end::schema-generation-domain-model-example[]
+}

documentation/src/test/resources/schema-generation.sql

@@ -0,0 +1 @@
+create sequence book_sequence start with 1 increment by 1

hibernate-core/src/main/java/org/hibernate/annotations/Formula.java

@@ -27,7 +27,7 @@
  * </pre></blockquote>
  *
  * <blockquote><pre>
- *     // call functions
+ *     // call database functions ( e.g. MySQL upper() and substring() )
  *     &#064;Formula( "upper( substring( middle_name, 1 ) )" )
  *     Character getMiddleInitial() { ... }
  * </pre></blockquote>