[jboss-user] [EJB3] - Concurrence management

[Alessandro Laurucci]

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

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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
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