The persistence in OpenNaaS is implemented through the following components:

• BBDD Module: Data Base HSQLDB (HyperSQL DataBase). Is a relational database engine written in Java. Can be found in the bundle of the folder, opennaas/core/hsqldb
  
  
• Persistence Module: Classes that provide the communication between the BBDD and the other application layers. This module implements the DAO pattern. Can be found in the folder opennaas/core/persistence. Through JPA specification and his implementation, OpenJPA, provides the mapping between business entities and relational tables.
  
  
  • GenericRepository: interface that defines, through generics, the essential methods to access the DB (find, save, delete…).
    
    
  • GenericJpaRepository: implements the interface GenericRepository and allows through the EntityManager access to DB.
    
    
  • GenericOSGiJpaRepository: class that extends of GenericJpaRepository. It contains the mechanisms to get the EntityManager from the OSGi container.

The classes that manage the persistence (e.g. ResourceDescriptorRepository) extend of GenericOSGiJpaRepository and execute the methods declared in the interface GenericRepository.

• Resources Module: Inside the bundle, opennaas/core/resources, is defined the persistence through the persistence.xml file and the core.xml (blueprint) file. In them we can see:
  
  
  • core.xml (blueprint): this file publish the datasource as a osgi service.
    
    
  • DataSource: the bean with the DataSource and the configuration parameters of the DB.
    
    
  • Service: the service that publish the DataSource in the OSGi container.
    
    
  • persistence.xml: this file has the persistence units.
    
    
    • The name of the persistence-unit. From this value the GenericOSGiJpaRepository obtains the EntityManager
      
      
    • Tag Non JTA DataSource: In this parameter we can find the global JNDI. With the JNDI the non-jta accesses to the datasource. (The non-JTA resource pattern is generally used when dealing with a single resource in the absence of global transactions. The non-JTA resource pattern is typically used within the scope of a web application or an application client. The application controls the transaction with the data source with the EntityTransaction interface.)
      
      
    • Classes to persist

The persisted entities must be annotated.