CODEWITHSUNDEEP
javahibernatehqljpql
user938069
user938069

Reputation:

how to query two different databases(on different servers) in a hql or jpql query?

I want to write a query on two tables in two distinct databeses(on two distinct database engines with same vendor) using hql or jpql? tblA in databaseA on mysql ServerA tblB in databaseB on mysql ServerB what solutions are there?

Upvotes: 4

Views: 1112

Answers (1)

smox
smox

Reputation: 315

Basically you have to get two session factories - one for each database (datasource). I found the following code at: http://www.java-forums.org/jdbc/867-hibernate-multiple-databases.html which should do the trick.

public class HibernateUtil {

    private static Log log = LogFactory.getLog(HibernateUtil.class);
    private static HashMap<String, SessionFactory> sessionFactoryMap = new HashMap<String, SessionFactory>();

    public static final ThreadLocal sessionMapsThreadLocal = new ThreadLocal();

    public static Session currentSession(String key) throws HibernateException {

        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();

        if (sessionMaps == null) {
            sessionMaps = new HashMap();
            sessionMapsThreadLocal.set(sessionMaps);
        }

        // Open a new Session, if this Thread has none yet
        Session s = (Session) sessionMaps.get(key);
        if (s == null) {
            s = ((SessionFactory) sessionFactoryMap.get(key)).openSession();
            sessionMaps.put(key, s);
        }

        return s;
    }

    public static Session currentSession() throws HibernateException {
        return currentSession("");
    }

    public static void closeSessions() throws HibernateException {
        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();
        sessionMapsThreadLocal.set(null);
        if (sessionMaps != null) {
            for (Session session : sessionMaps.values()) {
                if (session.isOpen())
                    session.close();
            };
        }
    }

    public static void closeSession() {
        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();
        sessionMapsThreadLocal.set(null);
        if (sessionMaps != null) {
            Session session = sessionMaps.get("");
            if (session != null && session.isOpen())
                session.close();
        }
    }

    public static void buildSessionFactories(HashMap<String, String> configs) {
        try {
            // Create the SessionFactory
            for (String key : configs.keySet()) {
                URL url = HibernateUtil.class.getResource(configs.get(key));
                SessionFactory sessionFactory = new Configuration().configure(url).buildSessionFactory();
                sessionFactoryMap.put(key, sessionFactory);
            }

        } catch (Exception ex) {
            ex.printStackTrace(System.out);
            log.error("Initial SessionFactory creation failed.", ex);
            throw new ExceptionInInitializerError(ex);

        } // end of the try - catch block
    }

    public static void buildSessionFactory(String key, String path) {
        try {
            // Create the SessionFactory
            URL url = HibernateUtil.class.getResource(path);
            SessionFactory sessionFactory = new Configuration().configure(url).buildSessionFactory();
            sessionFactoryMap.put(key, sessionFactory);

        } catch (Throwable ex) {

            log.error("Initial SessionFactory creation failed.", ex);
            throw new ExceptionInInitializerError(ex);

        } // end of the try - catch block
    }

} // end of the class

Upvotes: 1

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