Ajax调用使字段为空

updated the code but not real change.

When I set the player I want to update the other select one menu with the current players club. But the menu will become completely empty. The bean will always return the correct value.

Navigating from the page and back will show the correct value. It will then always work as intended after the first time you navigate back.

<p:selectOneMenu value="#{player}"
                converter="playerConverter" id="playerList">
            <f:selectItem itemLabel="---" noSelectionOption="true" />
            <f:selectItems value="#{servicePlayer.allPlayers}"
             var="n"
             itemValue="#{n}"
             itemLabel="#{n.combinedName}"
             itemLabelEscaped="true"/>
               <p:ajax event="change" execute="@this" update="ClubMenu" actionListener="#{serviceHCP.getClubs(player)}"/>  
              <!--  p:ajax event="change" execute="@this" render="ClubMenu" /-->
            </p:selectOneMenu>

                <h:outputText value="Klubb"></h:outputText>
                <p:selectOneMenu id="ClubMenu" value="#{serviceHCP.myClubList}" rendered="#{not empty serviceHCP.myClubList}">
                    <f:selectItems value="#{serviceHCP.getClubs(player)}" />
                </p:selectOneMenu>
                <h:outputText value="Serietyp"></h:outputText>

Backing bean function

public void getClubs(Player player) {

        if (factory == null) {
            factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
        }

        EntityManager em = factory.createEntityManager();

        //If we have a player just return that players club
        Query q;
        if (player == null || player.getClub() == null)
            q = em.createQuery("select t from Club t");
        else {
            q = em.createQuery("select t from Club t where t.id = :playerID");
            q.setParameter("playerID", player.getClub().getId());
        }

        myClubList = q.getResultList();
        for (Club aClub : myClubList) {
          System.out.println("Club list info: " + aClub);
        }
        System.out.println("Club Size: " + myClubList.size());

        em.close();
    }

You need to also process the playerList field:

<p:ajax process="@this" update="ClubMenu" />