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Concurrence management
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created by <a href="http://community.jboss.org/people/fox82">Alessandro Laurucci</a> in <i>EJB3</i> - <a href="http://community.jboss.org/message/612126#612126">View the full discussion</a>
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<div class="jive-rendered-content"><p>Hi to all,</p><p>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.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>I use this code:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p><span style="text-decoration: underline;"><strong>Table KGTWANAUSER01:</strong></span></p><p>-user (key)</p><p>-password</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p><strong style="text-decoration: underline;">Entity bean:</strong></p><p>import java.io.Serializable; </p><p>import javax.persistence.Column; </p><p>import javax.persistence.Entity; </p><p>import javax.persistence.Id; </p><p>import javax.persistence.Table; </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>@Entity @Table(name="KGTWANAUSER01") </p><p>public class User implements Serializable { </p><p>private static final long serialVersionUID = 1L; </p><p>@Id @Column(name="USER") private String USER; </p><p>@Column(name="PASSWORD") private String PASSWORD; </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public User(String us, String pswd) </p><p>{ this.user=us; this.password=pswd; } </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public String getUSER() </p><p>{ return USER; } </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public String getPASSWORD() </p><p>{ return PASSWORD; } </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public void setUSER(String uSER) </p><p>{ USER = uSER; } </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public void setPASSWORD(String pASSWORD) </p><p>{ PASSWORD = pASSWORD; } </p><p>}</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p><a class="jive-link-anchor-small">#</a></p><p><a class="jive-link-anchor-small"><p class="programlistingco"><span style="text-decoration: underline;"><strong>Stateless Session Bean (register method):</strong></span></p><p class="programlistingco">....</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>public String register(String user, String password)</p><p>   {  </p><p>      User us = new User (user, password)      </p><p>      List existing = em.createQuery(</p><p>         "select username from User where username = #{user.username}")</p><p>         .getResultList();</p><p>         </p><p>      if (existing.size()==0)</p><p>      {</p><p>         em.persist(us);</p><p>          return "OK";</p></a></p><p><a class="jive-link-anchor-small">#</a></p><p><a class="jive-link-anchor-small"><p style="display: inline !important;">      }       </p></a></p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>      else</p><p>      {</p><p>         return "NO;"</p><p>      }</p><p>   }</p><p>....</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco">My problem is this:</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco">I have two client A e B that want to create their new user, both with the username "ale":</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco">A call register method, execute the select, no other user "ale" are register so existing.size=0;</p><p class="programlistingco">B call the same method, and also in this case no other user "ale" are register so existing.size=0;</p><p class="programlistingco">A make em.persist(us) adn the transaction is OK</p><p class="programlistingco">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...</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco">Ho i can solve this problem?</p><p class="programlistingco">Thanks to All</p><p class="programlistingco" style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p class="programlistingco">Alessandro</p></div>
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