0 Replies Latest reply on Jun 27, 2011 10:14 AM by Alessandro Laurucci

    Concurrence management

    Alessandro Laurucci Newbie

      Hi to all,

      I'm developing my first EJB3 application with eclipse. I don't know i manage the insert into a database in case of duplicate key.

       

       

      I use this code:

       

      Table KGTWANAUSER01:

      -user (key)

      -password

       

       

      Entity bean:

      import java.io.Serializable;

      import javax.persistence.Column;

      import javax.persistence.Entity;

      import javax.persistence.Id;

      import javax.persistence.Table;

       

       

      @Entity @Table(name="KGTWANAUSER01")

      public class User implements Serializable {

      private static final long serialVersionUID = 1L;

      @Id @Column(name="USER") private String USER;

      @Column(name="PASSWORD") private String PASSWORD;

       

       

      public User(String us, String pswd)

      { this.user=us; this.password=pswd; }

       

       

      public String getUSER()

      { return USER; }

       

       

      public String getPASSWORD()

      { return PASSWORD; }

       

       

      public void setUSER(String uSER)

      { USER = uSER; }

       

       

      public void setPASSWORD(String pASSWORD)

      { PASSWORD = pASSWORD; }

      }

       

       

      Stateless Session Bean (register method):

      ....

       

      public String register(String user, String password)

         { 

            User us = new User (user, password)     

            List existing = em.createQuery(

               "select username from User where username = #{user.username}")

               .getResultList();

              

            if (existing.size()==0)

            {

               em.persist(us);

                return "OK";

            }      

       

            else

            {

               return "NO;"

            }

         }

      ....

       

       

      My problem is this:

       

      I have two client A e B that want to create their new user, both with the username "ale":

       

      A call register method, execute the select, no other user "ale" are register so existing.size=0;

      B call the same method, and also in this case no other user "ale" are register so existing.size=0;

      A make em.persist(us) adn the transaction is OK

      B try to make the insert with the persist, but the user now exist, so the application crashs and Jboss show me a list of errors caused by the duplicate key...

       

      Ho i can solve this problem?

      Thanks to All

       

      Alessandro