Document how to configure a component that Hibernate depends upon

Closes gh-6333

Author: wilkinsona

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

@@ -1881,6 +1881,27 @@ bean.
 
 
 
+[[howto-configure-a-component-that-is-used-by-JPA]]
+=== Configure a component that is used by JPA
+If you want to configure a component that will be used by JPA then you need to ensure
+that the component is initialized before JPA. Where the component is auto-configured
+Spring Boot will take care of this for you. For example, when Flyway is auto-configured,
+Hibernate is configured to depend upon Flyway so that the latter has a chance to
+initialize the database before Hibernate tries to use it.
+
+If you are configuring a component yourself, you can use an
+`EntityManagerFactoryDependsOnPostProcessor` subclass as a convenient way of setting up
+the necessary dependencies. For example, if you are using Hibernate Search with
+Elasticsearch as its index manager then any `EntityManagerFactory` beans must be
+configured to depend on the `elasticsearchClient` bean:
+
+[source,java,indent=0]
+----
+include::{code-examples}/elasticsearch/HibernateSearchElasticsearchExample.java[tag=configuration]
+----
+
+
+
 [[howto-database-initialization]]
 == Database initialization
 An SQL database can be initialized in different ways depending on what your stack is. Or

spring-boot-docs/src/main/java/org/springframework/boot/elasticsearch/HibernateSearchElasticsearchExample.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2012-2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.elasticsearch;
+
+import javax.persistence.EntityManagerFactory;
+
+import org.springframework.boot.autoconfigure.data.jpa.EntityManagerFactoryDependsOnPostProcessor;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Example configuration for configuring Hibernate to depend on Elasticsearch so that
+ * Hibernate Search can use Elasticsearch as its index manager.
+ *
+ * @author Andy Wilkinson
+ */
+public class HibernateSearchElasticsearchExample {
+
+	// tag::configuration[]
+	/**
+	 * {@link EntityManagerFactoryDependsOnPostProcessor} that ensures that
+	 * {@link EntityManagerFactory} beans depend on the {@code elasticsearchClient} bean.
+	 */
+	@Configuration
+	static class ElasticsearchJpaDependencyConfiguration
+			extends EntityManagerFactoryDependsOnPostProcessor {
+
+		ElasticsearchJpaDependencyConfiguration() {
+			super("elasticsearchClient");
+		}
+
+	}
+	// end::configuration[]
+
+}