How to connect to multiple nosql databases in Hibernate-ogm

Question

1. In my web app I need to connect to Mongodb and Neo4j, how to configure it?
2. and if I need to connect to Mongodb and Mysql , how to configure it?

Answer 1

You need to define different persistence units. For example, if you are using the persistence.xml file it will look something like:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>                                             
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="neo4j-pu">                                                                 
    <provider>org.hibernate.ogm.jpa.HibernateOgmPersistence</provider>                              
    <properties>                                                                                    
      <property name="hibernate.ogm.datastore.provider" value="neo4j_http"/>                                          
      ...
    </properties>                                                                                   
  </persistence-unit>

  <persistence-unit name="mongodb-pu">                                                                 
    <provider>org.hibernate.ogm.jpa.HibernateOgmPersistence</provider>                              
    <properties>                                                                                                             
      <property name="hibernate.ogm.datastore.provider" value="MONGODB"/>                           
      <property name="hibernate.ogm.datastore.database" value="ogm_test_database"/>                 
      <property name="hibernate.ogm.datastore.create_database" value="true"/>
      ...
    </properties>                                                                                   
  </persistence-unit>                    

  <persistence-unit name="mysql-pu">                                                                 
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>                                                                                                             
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpatestdb" />
      ...
    </properties>                                                                                   
  </persistence-unit>                                                                    
</persistence>    

At this point when you need the persistence factory or the entity manager you need to specify the name:

@PersistenceUnit(unitName = "neo4j-pu")
EntityManagerFactory neo4jEMF;

@PersistenceContext(unitName = "neo4j-pu")
EntityManager neo4jEM;

This isn't any different from what you would do with Hibernate ORM only or JPA. You can also do this via native API, but I think you got the idea.