Detached entity passed to persist (Objeto não quer persistir)

Programação Java
#1

O que siginifica detached entity ?

package erp.banco.agencia;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.PersistenceContext;

import erp.banco.Banco;
import javax.persistence.CascadeType;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;

@PersistenceContext(unitName = “depto”)
@Entity
@SuppressWarnings(“serial”)
public class Agencia implements Serializable {

@ManyToOne(cascade = CascadeType.ALL, fetch=FetchType.EAGER)
private Banco banco;
@Id
    @GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Column(length = 30)
private String nome;
@Column(length = 15)
private String numero;

public Agencia() {
        
}

public Banco getBanco() {
	return banco;
}


public Long getId() {
	return id;
}

public String getNome() {
	return nome;
}

public String getNumero() {
	return numero;
}

public void setBanco(final Banco banco) {
	this.banco = banco;
}

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

public void setNome(final String nome) {
	this.nome = nome;
}

public void setNumero(final String numero) {
	this.numero = numero;
}

@Override
public String toString() {
	return nome;
}

}

package erp.banco;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.PersistenceContext;

@PersistenceContext(unitName = “depto”)
@Entity
@SuppressWarnings(“serial”)
public class Banco implements Serializable {

@Column(length = 15)
private String codigo;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Column(length = 50)
private String nome;

public Banco() {

}

public String getCodigo() {
    return codigo;
}

public Long getId() {
    return id;
}

public String getNome() {
    return nome;
}

public void setCodigo(final String codigo) {
    this.codigo = codigo;
}

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

public void setNome(final String nome) {
    this.nome = nome;
}

@Override
public String toString() {
    return nome;
}

}

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: erp.banco.Banco
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1377)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1300)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1306)
at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:871)

#2 
@Override
public void salvarAgencia(final Agencia agencia) {
    EntityManager em = HibernateJpaUtil.getEntityManagerFactory()
            .createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();
    em.merge(agencia);
    tx.commit();
    em.close();

}

Resolvido
Substitui, em vez de usar:
em.persist(agencia);
usei
em.merge(agencia);