N pra N Hibernate

tenho essa tabela

@Entity @Table(name = "tipo_usuario") @NamedQueries({@NamedQuery(name = "TipoUsuario.findAll", query = "SELECT t FROM TipoUsuario t"), @NamedQuery(name = "TipoUsuario.findById", query = "SELECT t FROM TipoUsuario t WHERE t.id = :id"), @NamedQuery(name = "TipoUsuario.findByTipo", query = "SELECT t FROM TipoUsuario t WHERE t.tipo = :tipo")}) public class TipoUsuario implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Basic(optional = false) @Column(name = "id", nullable = false) private Integer id; @Basic(optional = false) @Column(name = "tipo", nullable = false) private int tipo; @JoinTable(name = "permissao", joinColumns = {@JoinColumn(name = "id_tipo", referencedColumnName = "id", nullable = false)}, inverseJoinColumns = {@JoinColumn(name = "id_sessao", referencedColumnName = "id", nullable = false)}) @ManyToMany(mappedBy = "tipoUsuarioList") private List<Sessao> sessaoList;

que é ligada N pra N com essa tabela

@Entity @Table(name = "sessao") @NamedQueries({@NamedQuery(name = "Sessao.findAll", query = "SELECT s FROM Sessao s"), @NamedQuery(name = "Sessao.findById", query = "SELECT s FROM Sessao s WHERE s.id = :id"), @NamedQuery(name = "Sessao.findBySessao", query = "SELECT s FROM Sessao s WHERE s.sessao = :sessao")}) public class Sessao implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Basic(optional = false) @Column(name = "id", nullable = false) private Integer id; @Basic(optional = false) @Column(name = "sessao", nullable = false, length = 45) private String sessao; @JoinTable(name = "permissao", joinColumns = {@JoinColumn(name = "id_sessao", referencedColumnName = "id", nullable = false)}, inverseJoinColumns = {@JoinColumn(name = "id_tipo", referencedColumnName = "id", nullable = false)}) @ManyToMany private List<TipoUsuario> tipoUsuarioList;

quero gerar a tabela relacional permissao que tem o id_sessao e o id_tipo_usuario eu consigo pesquisar mas na hora de inserir nao funciona ele nao grava na tabela permissao do banco os dois id’s…

o que eu tenho que fazer pra gravar uma tabela relacional N pra N??