更新/删除查询中的javax.persistence.TransactionRequiredException

Question

I am working on a simple application where the records of users in a database are displayed in a primefaces datatable and the user can edit or delete the records. Here is the jsf file

<h:form>
            <p:dataTable var="user" value="#{userBean.users}" >
                <p:column headerText="username">
                    <h:inputText value="#{user.username}" rendered="#{userBean.editable}" />
                    <h:outputText value="#{user.username}" rendered="#{not userBean.editable}" />
                    <!--<h:outputText value="#{user.username}" />-->
                </p:column>

                <p:column headerText="edit">
                    <h:commandLink value="Edit" action="#{userBean.editAction(index)}" rendered="#{not userBean.editable}" />
                </p:column>

                <p:column headerText="save">
                    <p:commandButton value="Save" id="save" disabled="false" action="#{userBean.saveAction(user)}"/>
                </p:column>

                <p:column headerText="delete">
                    <p:commandButton value="Delete" id="delete" disabled="false" action="#{userBean.deleteAction(user)}"/>
                </p:column>

            </p:dataTable>

        </h:form>

and here is the save and update action methods i am calling in the bean

public String saveAction(User user) {

    this.setEditable(false);
    DB db = new DB();
    db.updateUser(user);
    return "editSuccess";
}

public String deleteAction(User user) {

    DB db = new DB();
    db.deleteUser(user);
    return "editSuccess";
}

and here are the methods in the dao layer

EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("RegisterationFormJPAPU");
EntityManager em = emf.createEntityManager();
public void updateUser(User user) {
    Query query = em.createQuery("update User set username = :uname where username = :uname");
    query.setParameter("uname", user.getUsername());
    query.executeUpdate();
}

public void deleteUser(User user) {
    Query query = em.createQuery("delete from User where username = :uname");
    query.setParameter("uname", user.getUsername());
    query.executeUpdate();
}

But when i press the edit link or the delete button, this error appears

    Severe:   javax.faces.el.EvaluationException: javax.persistence.TransactionRequiredException: 
Exception Description: No transaction is currently active

Would anyone tell me where is the problem.

Answer 1

Pleased try this:

em.getTransaction().begin();
   Query query = em.createQuery("update User set username = :uname where username = :uname");
    query.setParameter("uname", user.getUsername());
    query.executeUpdate();
    em.getTransaction().commit();

and let me know if this solves your problem.

Answer 2

You cannot explicitly call the transaction in this context. The commit is managed by the server automatically.

You can simply use:

user.setName("NEW USER NAME"); 
modifyUser(user); 

public void modifyUser(User user) {
     em.merge(user)}