[jboss-user] [EJB3] - Concurrence management

Alessandro Laurucci [http://community.jboss.org/people/fox82] created the discussion "Concurrence management" To view the discussion, visit: http://community.jboss.org/message/612126#612126 -------------------------------------------------------------- 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 -------------------------------------------------------------- Reply to this message by going to Community [http://community.jboss.org/message/612126#612126] Start a new discussion in EJB3 at Community [http://community.jboss.org/choose-container!input.jspa?contentType=1&...]