TransactionRequiredException for UPDATE query ?

From: Arun Gupta <Arun.Gupta_at_Sun.COM>
Date: Thu, 25 Oct 2007 21:54:53 -0700

I've the following code fragment in a JSP:

-- cut here --
   EntityManagerFactory emf =
Persistence.createEntityManagerFactory("WebApplication1PU");
   EntityManager em = emf.createEntityManager();

   String update = request.getParameter("update");
   if (Boolean.parseBoolean(update)) {
       String isbn = request.getParameter("isbn");
       String description = request.getParameter("description");

             int result = em.createNamedQuery("Books.updateDescription").
             setParameter("isbn", isbn).
             setParameter("description", description).
             executeUpdate();
             out.println(result + " entities updated.");
   }
-- cut here --

Books.updateDescription is:

@NamedQuery(name = "Books.updateDescription", query = "UPDATE Books b
SET b.description= :description WHERE b.isbn = :isbn")

If I try to invoke the page as:

http://localhost:8080/WebApplication1/data.jsp?update=true&isbn=123456&description=How%20to%20train%20for%20a%20marathon%20%3FThu%20Oct%2025%202007%2021%3A28%3A26%20GMT-0700%20(Pacific%20Daylight%20Time)

then I get the exception:

javax.persistence.TransactionRequiredException:
Exception Description: No transaction is currently active

This is not an issue if I replace updateDescription with another query
that uses only SELECT. Do I need special transactions when UPDATE query
is invoked ?

I could not find any reference in the JavaEE5 tutorial
(http://java.sun.com/javaee/5/docs/tutorial/doc/bnbtl.html#bnbud) on
this topic.

-Arun

-- 
Web Technologies and Standards
Sun Microsystems, Inc.
Blog: http://blogs.sun.com/arungupta