org.hibernate.MappingException: Unknown entity: sk.banik.app.myfirstapp.model.Person
   org.hibernate.impl.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:550)
   org.hibernate.impl.SessionImpl.getEntityPersister(SessionImpl.java:1338)
   org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:98)
   org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
   org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
   org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
   org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
   org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
   org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)

package sk.banik.app.myfirstapp.model;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import org.jboss.seam.annotations.Name;

@Entity
@Table(name = "person")
@Name("person")
public class Person implements Serializable {

    @Id
    @GeneratedValue
    @Column(name = "ID")
    private int id;
   
    @Column(name = "firstName", length = 30)
    private String firstName;

    @Column(name = "lastName", length = 30)
    private String lastName;

    @Column(name="userName", length = 30)
    private String userName;

    @Column(name="password", length = 30)
    private String password;
   
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "person")
    private List<Account> accounts = new ArrayList<Account>();

    public Person() {
    }

    public int getId() {
        return this.id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return this.firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return this.lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public List<Account> getAccounts() {
        return this.accounts;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }
   
}

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>

<session-factory   name= "java:/sessionFactory">
         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
         <property name="transaction.flush_before_completion">true</property>
         <property name="connection.release_mode">after_statement</property>
         <property name="transaction.manager_lookup_class">org.hibernate.transaction.JBossTransactionManagerLookup</property>
         <property name="transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</property>
         <property name="connection.datasource">java:/dataSource</property>
</session-factory>

</hibernate-configuration>

@Stateful
@Name("personAction")
public class PersonAction implements PersonService, Serializable{

   
    @In
    private Session hibernateSession;

    @DataModelSelection
    @Out(required = false)
    private Person active;

    @DataModel(scope = ScopeType.PAGE)
    private List<Person> personsList;
           
    @Transactional(TransactionPropagationType.REQUIRED)
    @Override
    public void addPerson(Person person){
        hibernateSession.save(person);
        active = person;
        FacesMessages.instance().add("New person with name: #{active.fisrtName},#{active.lastName} was saved");
        getAllPersons();
    }